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Qpopper Home


Qpopper Information

Frequently Asked
Questions (FAQ)


Current Release

Mirror sites

Bug Reports

Installation and Documentation

Submitting Patches


License and Legal Information

The GUIDE.pdf file

Qpopper on Linux

Security Vulnerability


The most widely-used POP3 server for UNIX, Linux, etc.

Qpopper 4.1 is now available. 

Still using version 2.53? Read up on the benefits of 3.0 and 3.1 before you move to 4.1.

Qpopper 4.1 now available.

Qpopper 4.1 has many new features, including:

  • IPv6 support
  • Significantly improved performance
  • Cygwin compatibility (for use under Windows)
  • Ability to execute arbitrary programs when users log in
  • And lots more
  • Download the software archive (as a .tar.Z or a .tar.gz file) from QUALCOMM's ftp site, or from a Mirror site

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    Features introduced in Qpopper 4.0:

    • Mac OS X compatibility
    • Faster start-up (1,000 times faster, in many cases)
    • Reduced I/O at session end (one-third less!)
    • TLS/SSL (allows authentication and email to be strongly encrypted between any TLS/SSL-enabled mail client and Qpopper; requires TLS/SSL)
    • Plus all the great features of Qpopper 3.1 (including full sources)
    • Most compile-time options now are available at run-time
    • Easier administration

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    Download alpha and beta builds as they become available from the 'beta' directory in QUALCOMM's ftp site, or from a Mirror site

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    What is Qpopper?
    Qpopper is the most widely-used server for the POP3 protocol (this allows users to access their mail using any POP3 client).  Qpopper supports the latest standards, and includes a large number of optional features.  Qpopper is normally used with standard UNIX mail transfer and delivery agents such as sendmail or smail.

    Qpopper's goals are: security, stability, safety, features, and performance.

    The 3 and later code base has multiple levels of protection again common security vulnerabilities, so even if there is a bug at one level, the other levels can protect against an exploit.  Stability means running without crashing or other problems.  All bug reports are reviewed and taken seriously.  Safety means protecting the user's mail.  Qpopper takes extra precautions to guard against spool corruption, even if there is a system crash or power failure during an update.  Qpopper provides a large number of features, such as bulletins, support for wireless devices, APOP, integration with packages such as Kerberos, drac, etc.  Qpopper strives for the maximum possible performance consistent with safety.  You can also tell Qpopper when it is running in an environment where some precautions are not required, resulting in extra performance (for example, if users do not access mail using shell accounts).

    This server is fully compliant with RFC 1939 (which defines the POP protocol) and RFC 2449 (which defines the POP extension mechanism and the extended response codes), and works with all known POP3 clients.

    Qpopper also supports Kerberos V4 and V5 if enabled.  You can obtain a Kerberos engine for your system from the MIT Kerberos Distribution Page.

    If you use Kerberos with Qpopper, be sure to obtain updated libraries that address CERT Advisory CA-2000-06.

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    Current Qpopper Release

    The latest official release of Qpopper is 4.1.  All Qpopper users should consider upgrading.  4.1 supports IPv6 and has a number of improvements. 

    Versions of Qpopper older than 3.0 may contain a security vulnerability.  Please upgrade to the current release.

    These versions are available as software archives (.tar.Z or .tar.gz files) at QUALCOMM's ftp site, or from a Mirror site

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    Mirror Sites
    For faster connections, please choose the site closest to you.

    Known Mirror Sites:

    • Australia FTP (only accessible in Australia and New Zealand)
    • Japan (Ibaraki) HTTP
    • Japan (Tokyo, Ibaraki, Iwate, Kyoto, Osaka, Sendai, Toyama and so on -- Japan Round robin) HTTP
    • Taiwan (HsinChu) FTP
    • U.K. FTP
    • U.S. FTP HTTP

    If you would like to mirror the Qpopper FTP and/or HTTP site, please send email to  Thank you.

    (Of course, these aren't really mirrors, because that would mean they stored all the bits backwards, which wouldn't be of much use, would it?  But we call them mirrors just the same.)

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    Bug Reports

    Please read the FAQ if you have any questions.  This list is continuously updated.  If you find any errors or omissions, please write to

    While all messages are read and all constructive suggestions are considered for development, because of time and resource limitations, we can't answer all messages.

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    Installation and Documentation

    The file GUIDE.pdf gives detailed installation instructions.  Please read the entire file before installing Qpopper on your system.  This file also tells you how to configure Qpopper, and how to change any of the default settings.

    If you want to get started quickly, run the ./configure script to generate a Makefile for your platform and then type make.

    If you use shadow passwords (and most sites do these days) you might need to add --enable-specialauth to the ./configure command. For example, ./configure --enable-specialauth

    However, in most cases configure is able to detect when this is needed and automatically add it.

    See the GUIDE.pdf file for details.

    Detailed documentation is available in the doc directory.  In particular, the file doc/Release.Notes describes the changes from one version to the next.

    For beta versions, the file doc/Changes lists the changes from one beta release to the next.

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    Submitting Patches for Qpopper

    We welcome patches from the user community. Patches that address common issues which affect or interest many sites are most likely to be integrated into the Qpopper release.

    The less time we have to spend rewriting a patch, the sooner it can be incorporated into Qpopper. Therefore, please fit your patch against the current highest codeline, which may be an alpha or beta (feel free to email an enquiry before finishing a patch, especially one that is large or complex). Also, please make sure your patch adheres to our simple coding guidelines.

    Note that all patches submitted become the property of QUALCOMM Incorporated, and if included in Qpopper will be covered by the standard license agreement. By submitting a patch you assert that you have the authority to transfer ownership to us.

    Send patches to

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    Qpopper is the result of the work of many individuals and organizations around the world.  The original development was done around 1989 at UC Berkeley and many have contributed since.

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    Qpopper on Linux

    Linux users should not use versions of Qpopper older than 3.0.

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    Security Vulnerability
    Some versions of Qpopper are vulnerable to buffer overruns.  Qpopper 2.41 and older can be used to obtain root access to your system.  Qpopper 2.53 and older may permit an attacker who has access to a valid account to obtain a shell with group-id 'mail', potentially allowing read/write access to all mail. 

    All users of Qpopper are urged to upgrade to the current version.

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