Managing IMAP (Dianna Mullet, Kevin Mullet) (Z-Library)

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Managing IMAP

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Managing IMAP Dianna Mullet & Kevin Mullet Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo

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Managing IMAP by Dianna Mullet and Kevin Mullet Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Printed in the United States of America. Published by O’Reilly & Associates, Inc., 101 Morris Street, Sebastopol, CA 95472. Editor: Mike Loukides Production Editor: Melanie Wang Cover Designer: Ellie Volckhausen Printing History: September 2000: First Edition. Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of O’Reilly & Associates, Inc. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and O’Reilly & Associates, Inc. was aware of a trademark claim, the designations have been printed in caps or initial caps. The association between the image of a bushbuck and IMAP is a trademark of O’Reilly & Associates, Inc. While every precaution has been taken in the preparation of this book, the publisher assumes no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. Library of Congress Cataloging-in-Publication Data Mullet, Dianna Managing IMAP/Dianna Mullet & Kevin Mullet. p. cm. Includes index. ISBN 0-596-00012-X 1. Electronic mail systems 2. Internet programming. I. Mullet, Kevin. TK5105.73 .M84 2000 005.7'1376--dc21 00-064970 ISBN: 0-596-00012-X [M]

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v Oracle 8i Internal Services for Waits, Latches, Locks, and Memory, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Table of Contents Foreword ................................................................................................................. xi Preface .................................................................................................................. xiii I. IMAP Fundamentals .......................................................................... 1 1. The Internet Mail Model ......................................................................... 3 What Is the Internet Mail Model? .................................................................... 3 Why Follow the Internet Mail Model? ........................................................... 10 Examples ........................................................................................................ 12 2. What Is IMAP? .......................................................................................... 16 IMAP in a Nutshell ......................................................................................... 16 IMAP’s Three Interaction Models .................................................................. 17 Why IMAP? ..................................................................................................... 20 IMAP and POP: A Comparison ..................................................................... 24 Present and Future of IMAP .......................................................................... 32 Open Source Server Implementations .......................................................... 33 IMAP-Related Standards and Documents ..................................................... 35 3. Anatomy of an IMAP Session ............................................................ 37 IMAP Session Concepts ................................................................................. 37 IMAP Components ......................................................................................... 39 An IMAP Session Play-by-Play ...................................................................... 42

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vi Table of Contents Oracle 8i Internal Services for Waits, Latches, Locks, and Memory, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. II. IMAP Mail User Agents (MUAs) .............................................. 49 4. IMAP Clients ............................................................................................. 51 Client Features ................................................................................................ 51 PINE and PC PINE ......................................................................................... 55 Star Mail .......................................................................................................... 61 Netscape Messenger ....................................................................................... 66 Outlook Express ............................................................................................. 69 Mulberry ......................................................................................................... 71 Eudora ............................................................................................................ 75 Other Clients .................................................................................................. 77 5. Web-Based IMAP Clients ....................................................................... 79 What’s a Web-Based IMAP Client? ................................................................ 79 Why Use a Web-Based IMAP Client? ............................................................ 80 Web IMAP Clients .......................................................................................... 83 IMP .................................................................................................................. 84 Mailspinner ..................................................................................................... 89 SilkyMail ......................................................................................................... 93 EMU 3 ............................................................................................................. 96 WING ............................................................................................................ 101 III. The Cyrus IMAP Server ............................................................... 105 6. Introduction to the Cyrus IMAP Server ........................................ 107 History of Cyrus ........................................................................................... 108 Cyrus Concepts and Features ...................................................................... 111 Cyrus Server Configuration .......................................................................... 118 The Future of Cyrus ..................................................................................... 121 Strengths and Weaknesses of Cyrus ........................................................... 122 When Is Cyrus the Right Choice? ................................................................ 123 7. Installing the Cyrus IMAP Server ................................................... 125 Software Prerequisites .................................................................................. 125 Hardware Note ............................................................................................. 126 Where to Get the Software .......................................................................... 127 Supported Platforms .................................................................................... 128 Installing Cyrus ............................................................................................. 128 Upgrading from Previous Versions of Cyrus IMAP .................................... 133

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Table of Contents vii Oracle 8i Internal Services for Waits, Latches, Locks, and Memory, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Components of Cyrus and What They Do ................................................. 134 Common Problems ...................................................................................... 136 Significant Bugs ............................................................................................ 136 8. Configuring the Cyrus Server .......................................................... 137 IMAP Configuration File and Directory ...................................................... 137 Configuring the Authentication Mechanism ............................................... 141 Configuring syslog ....................................................................................... 145 Configuring the MTA ................................................................................... 145 Getting Cyrus Up and Running ................................................................... 151 Testing Your Server ..................................................................................... 151 9. Cyrus System Administration .......................................................... 154 Cyrus System Administration with cyradm ................................................. 154 Common Tasks ............................................................................................. 156 Batch Account Maintenance with cyradm .................................................. 163 Shared Folders and Bulletin Boards ............................................................ 167 Mailstore Partitioning ................................................................................... 171 Quota Maintenance ...................................................................................... 173 Disaster Recovery ......................................................................................... 174 Migration from Berkeley (Unix) Mailbox Format to Cyrus ........................ 179 Mail Forwarding and Filtering on a Black Box .......................................... 191 Usenet Integration ........................................................................................ 197 Troubleshooting ........................................................................................... 199 Adding SSL Support to Cyrus ...................................................................... 201 IV. The UW IMAP Server .................................................................... 203 10. Introduction to the UW IMAP Server ............................................ 205 What Is UW IMAP? ....................................................................................... 205 UW’s Strengths ............................................................................................. 208 UW’s Limitations .......................................................................................... 209 UW IMAP Concepts ..................................................................................... 211 Does UW IMAP Match Your Needs? ........................................................... 217 11. Installing UW IMAP ............................................................................. 223 Where Do You Get UW IMAP? ................................................................... 223 What Do You Get with UW IMAP? ............................................................. 227 How Do You Install It? ................................................................................ 229 Where Can You Go for Help If You Get Stuck? ........................................ 233

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viii Table of Contents Oracle 8i Internal Services for Waits, Latches, Locks, and Memory, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. 12. UW System Administration .............................................................. 234 General Issues .............................................................................................. 234 Authentication .............................................................................................. 236 Security ......................................................................................................... 238 UW IMAP Utilities ........................................................................................ 240 V. Other Topics ........................................................................................ 243 13. Addressing IMAP Security ................................................................. 245 Security Resources ....................................................................................... 246 A Handful of Security Tips .......................................................................... 249 Monitoring Security ...................................................................................... 258 Boiling It All Down ...................................................................................... 260 14. Running a Dedicated Server ............................................................ 261 What’s a Dedicated Server? .......................................................................... 261 Account Provisioning ................................................................................... 261 Mission Restriction ....................................................................................... 272 The Ultimate in Dedicated Servers .............................................................. 276 15. Server-Side Mail Filtering ................................................................... 277 Why Filter on the Server? ............................................................................ 277 Procmail ........................................................................................................ 278 Sieve .............................................................................................................. 283 To Filter or Not to Filter… ........................................................................... 286 16. Server Performance Tuning .............................................................. 288 Platform ........................................................................................................ 288 I/O Subsystem Tuning ................................................................................. 291 Memory Tuning ............................................................................................ 295 Kernel and Network Driver Tuning ............................................................ 296 How to Know When It’s Time to Scale Up ................................................ 301 Running imapd: inetd Versus Standalone ................................................... 305 Charting It Up for the Suits ......................................................................... 306 17. Remote Configuration Storage ........................................................ 307 Why Store Client Configurations on a Server? ............................................ 307 IMSP, ACAP, or LDAP? ................................................................................. 309 IMSP .............................................................................................................. 311 ACAP ............................................................................................................. 314

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Table of Contents ix Oracle 8i Internal Services for Waits, Latches, Locks, and Memory, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. 18. IMAP Tools ............................................................................................... 319 IMAP Administration Tools .......................................................................... 319 Authentication Tools .................................................................................... 326 Monitoring and Testing Tools ..................................................................... 332 IMAP Clustering ........................................................................................... 338 IMAP APIs ..................................................................................................... 340 VI. Appendixes .......................................................................................... 347 A. Conversion from Berkeley Mail Format to Cyrus: Tools ....... 349 B. Adding SSL Support to IMAP ............................................................ 357 C. IMAP Commands .................................................................................. 362 Index .................................................................................................................... 381

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xi This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Bleeding Tab Text Foreword For nearly 10 years after I invented IMAP, it was called “the best-kept secret in electronic messaging.” Then, around 1995, key electronic messaging software ven- dors became convinced of its advantages over the older Post Office Protocol (POP), and IMAP’s presence in the industry exploded. Today, IMAP has evolved into a mature, widely deployed protocol. Even longtime proponents of POP have jumped on the IMAP bandwagon. More and more users are demanding IMAP, because IMAP is the only message access protocol that has the flexibility to accommodate their needs. These users are part of a growing trend to access the Internet from a variety of dif- ferent computers, appliances, and access paths. In one day, they may use a dialup from home; a wireless link on the bus, train, or ferry; and a super-high-capacity Internet2 link at the office. They may use a laptop while traveling and a desktop at home and work. They may be students using shared machines in a PC lab, with no personal data kept on the PC. These users have more advanced needs for messaging than a single incoming mailbox that is periodically downloaded to a single computer. They may have a large archive of messages in a multitude of mailboxes that they need to reference at any time and in any place. They may participate in bulletin boards or other shared message collections (e.g., a shared “customer service” mailbox). It could be any or all of the above. The common thread in these needs is highly diverse mail access patterns and needs. No matter how many different computers,

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xii Foreword This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. network connections, or mailboxes one uses, IMAP offers the flexibility needed for effective access. The trend is clear. The word is spreading to those email users who are not yet familiar with IMAP’s benefits. Corporate and ISP email providers are feeling the pressure to upgrade their services. Many server administrators, comfortable with a POP-only facility for many years, now find themselves playing catch-up. Understanding the requirements of the task, much less planning how to do it, can be daunting. Fortunately, the “doing it” part is relatively painless once the way is pointed out. Kevin and Dianna Mullet have done an outstanding job of presenting practical information on how to install, configure, and manage an IMAP server system. Both major freeware server implementations are covered in detail. I am particularly impressed by how the Mullets have uncovered and fleshed out useful information from mailing list folklore or passing mention in documenting. A book like this has been needed for a long time. It belongs on every server administrator’s bookshelf. —Mark Crispin Seattle, Washington 1 July 2000

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xiii This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Preface This book is both an overview of the IMAP protocol as well as a comprehensive installation and management guide for the two leading Unix-based IMAP servers. The University of Washington IMAP server, written by Mark Crispin, the father of the IMAP protocol, is an easy-to-install server that auto-detects and adapts to numerous mailstore formats on an individual user basis. The Cyrus IMAP server, from Carnegie Mellon University, is a high-performance, scalable server embraced by many larger sites. As important as IMAP is to the growth of email, we were very surprised to find that a book on IMAP hadn’t already been written—at least we couldn’t find one. There was a lot of disconnected information out on the Net in various documents in documentation included with source distributions, on web sites, buried inside archives for mailing lists, and in Usenet newsgroups, but there was very little cen- tralized assistance for the system administrator who wanted information on IMAP protocol, server administration, system design, and troubleshooting all in one place. This book is directed at Unix and email system administrators who are (or might be) using IMAP to get email from their central mailstore to their users’ client soft- ware. If you have five email users or five hundred thousand, we describe a system in this book that would meet your needs. If your users are all using a common platform like Microsoft Windows, Solaris, or Mac OS, or if none of your users have access to anything but a web browser, we outline ways to provide reliable, robust, manageable, and consistently powerful email service to each of your users. We’re true believers in IMAP because we’ve found that with a well-designed IMAP system, end-user email frustration is only directed at the content of their email, not at the quality of the service.

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xiv Preface This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. How This Book Is Organized Part I, IMAP Fundamentals The first three chapters introduce IMAP. They explain what IMAP is, how it fits into the world of email, and how it works. The rest of the book is organized into four parts. Part II, IMAP Mail User Agents (MUAs) Chapters 4 and 5 cover IMAP clients and web-based IMAP clients. Part III, The Cyrus IMAP Server Chapters 6 through 9 cover the Cyrus IMAP server. Part IV, The UW IMAP Server Chapters 10 through 12 cover the University of Washington (UW) IMAP server. Part V, Other Topics Chapters 13 through 18 cover miscellaneous important topics that are related to maintaining a robust and reliable IMAP server. Part VI, Appendixes We’ve included three appendixes in the book. Appendix A, Conversion from Berkeley Mail Format to Cyrus: Tools, is a list of tools that will aid in the con- version from Berkeley Mail format to Cyrus. Appendix B, Adding SSL Support to IMAP, is useful for those readers who want to add SSL support to IMAP. And Appendix C, IMAP Commands, is a list of IMAP commands. Conventions Used in This Book Italic is used for: • Email addresses • Uniform Resource Locators (URLs) • Program names • Protocol commands • Filenames and directory pathnames Constant width is used for: • Computer output in examples and text • Source code examples Constant width bold is used for: • Program invocation commands

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Preface xv This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Related Books sendmail, Bryan Costales with Eric Allman (O’Reilly) Essential System Administration, Æleen Frisch (O’Reilly) Programming Internet Email, David Wood (O’Reilly) We’d Like to Hear From You We have tested and verified the information in this book to the best of our ability, but you may find that features have changed (or even that we have made mis- takes!). Please let us know about any errors you find, as well as your suggestions for future editions, by writing to: O’Reilly & Associates, Inc. 101 Morris Street Sebastopol, CA 95472 1-800-998-9938 (in the U.S. or Canada) 1-707-829-0515 (international/local) 1-707-829-0104 (fax) You can also send us messages electronically. To be put on the mailing list or request a catalog, send email to: info@oreilly.com To ask technical questions or comment on the book, send email to: bookquestions@oreilly.com We have a web site for the book, where we’ll list examples, errata, and any plans for future editions. You can access this page at: http://www.oreilly.com/catalog/mimap/ For more information about this book and others, see the O’Reilly web site: http://www.oreilly.com Acknowledgments We would like to thank our editor, Mike Loukides, for his enthusiasm, patience, and guidance in taking on this project with a couple of fledgling authors. We would also like to thank Amos Gouaux, Walter Wong, Jon Forrest, and Mark Crispin, the father of IMAP, for their insightful reviews and recommendations. The book would not be complete without their input and astute insight. We’d also like to thank Mark Crispin for offering to write the foreword; we’re honored and pleased to have his contribution.

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This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. I I. MAP Fundamentals

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3 This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Chapter 1 In this chapter: • What Is the Internet Mail Model? • Why Follow the Internet Mail Model? • Examples 1 The Internet Mail Model IMAP stands for Internet Mail Access Protocol. For much of the Internet email sys- tem administrator community, it also stands for flexibility, speed, and power. These attributes come from abilities like being able to store all a user’s mail cen- trally, not demand that she store copies of it on each workstation from which she wants to access her mail. IMAP users also store their mail in an arbitrary number of server-side mailboxes, each of which they can move messages into or out of with any IMAP client. When an IMAP user checks her mail, her client need only download some of the header for each message, not the entire message. When she sees messages in her index she wants to retrieve, she can decide which parts of the 13-part message she wants to download, and which she doesn’t. These are capabilities that no other standardized mail access protocol permits. Before we dive into a more detailed discussion of IMAP, though, let’s talk about Internet mail in general. Much of this discussion is a definition of terms. In defin- ing those terms, however, we’re discussing the language that is the bedrock of Internet electronic mail. What Is the Internet Mail Model? The Internet Mail Model, like the Internet itself, is a collection of standardized components all acting with a common goal. In the case of email, the goal is to provide the framework for carrying electronic messages between one user and another. Each of the end users may be on very different platforms. Their respec- tive sites may have vast geographic, technological, and social differences. Those differences demand that the framework be at once both robust and flexible. The Internet’s email framework consists of agents, mailstores, and standards. It may help you to reference Figure 1-1 as you read the chapter. The figure shows how the agents, mailstores, and standards work together.

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4 Chapter 1: The Internet Mail Model This is the Title of the Book, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. The Agents (MUA, MTA, MDA) The software programs that handle Internet messages are called agents. There are three types of Internet messaging agents: the Mail Transport Agent (MTA), Mail Delivery Agent (MDA), and Mail User Agent (MUA). MTA An MTA (Figure 1-2) is a program that transmits and receives messages between messaging sites. The sending MTA accepts messages from end user client software and transmits it to a receiving MTA. The receiving MTA receives messages from the sending MTA, determines whether or not the recipient resides locally on the receiving MTA (server) system, and then hands off the message for delivery. If the message is destined for a user on the receiving MTA’s system, then the receiving MTA hands the message off to a Message Delivery Agent (MDA) such as /bin/mail. If the user is not on the local system, then the receiving MTA acts as a sending MTA to pass the message on to the MTA on the remote system. Figure 1-3 shows typical Internet message headers. Each “Received” header line represents transit through a separate MTA. MTAs do not touch the mailstore. They delegate that work to the MDA. MDA The MDA is the trench soldier: the grunt of Internet messaging. All the MDA knows is how to determine which local user the message is destined for and how to put the message in the correct place in the mailstore. Actually, that’s not quite all the MDA knows. Some super-charged MDAs, such as Procmail, have vast delu- sions of grandeur, but we’ll cover that later in the book. All that’s essential to know right now is that the MTA hands the MDA each Internet message destined for a local user and that the MDA is responsible for knowing where to place it in the mailstore. Figure 1-1. Email cycle of life Mail Access (retrieve)MTA MDA Mailstore Server-side MUA (popd, imapd) Mail Access (store) Mail Transfer MUA Compose and Encode Mail MUA Mail Server