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E-MailRelay is a simple SMTP proxy and relay MTA, written in C++, for Linux and Windows. When running as a proxy all e-mail messages can be passed through a user-defined program, such as a spam filter, which can drop, re-address or edit messages as they pass through. When running as a store-and-forward MTA incoming messages are stored in a local spool directory, and then forwarded to the next SMTP server on request.

Because of its functional simplicity E-MailRelay is easy to configure, often
only requiring the address of the target SMTP server to be put on the command line.

E-MailRelay can also run as a POP3 server. Messages received over SMTP can be automatically dropped into several independent POP3 mailboxes.

C++ source code is available for Linux, FreeBSD, MacOS X etc, and Windows. Distribution is under the GNU General Public License V3.

Quick start

To use E-MailRelay in store-and-forward mode use the "--as-server" switch to start the storage daemon in the background, and then trigger delivery of spooled messages by running with the "--as-client" switch and the address of the target host.

For example, to start a storage daemon listening on port 10025 use a command like this:

emailrelay --as-server --port 10025 --spool-dir /tmp

And then to forward the spooled mail to "smarthost" run something like this:

emailrelay --as-client smarthost:smtp --spool-dir /tmp

To get behaviour more like a proxy you can add the "--poll" switch so that messages are forwarded continuously rather than on-demand. This example starts a store-and-forward server that forwards spooled-up e-mail every hour:

emailrelay --as-server --poll 3600 --forward-to smarthost:smtp

For a proxy server that forwards each message as it is being received, without any delay, you can use the "--as-proxy" mode:

emailrelay --as-proxy smarthost:smtp

If you want to edit or filter e-mail as it passes through the proxy then specify your pre-processor program with the "--filter" switch, something like this:

emailrelay --as-proxy smarthost:smtp --filter /usr/local/bin/addsig

To run E-MailRelay as a POP server without SMTP use "--pop" and "--no-smtp":

emailrelay --pop --no-smtp --log --close-stderr

The "emailrelay-submit" utility can be used to put messages straight into the spool directory so that the POP clients can fetch them.

Note that by default E-MailRelay will always reject connections from remote machines. To allow connections from anywhere use the "--remote-clients" switch, but please consider the implications if your machine is connected to the Internet.

For more information on the command-line options refer to the reference guide or run:

emailrelay --help --verbose


The following documentation is provided:
· README -- this document
· COPYING -- the GNU General Public License
· INSTALL -- build & install instructions (including the GNU text)
· AUTHORS -- authors, credits and additional copyrights
· copyright -- main copyright and GPL reference
· userguide.txt -- user guide
· reference.txt -- reference document
· ChangeLog -- change log for releases

Source code documentation will be generated when building from source if "doxygen" is available.


Recent releases were developed on Ubuntu Linux 7.10 using:
· linux 2.6.22
· gcc 4.1.3
· autoconf 2.61

and on Windows NT4 SP6 using:
· MSVC 6.0 SP3

The code was originally developed on SuSE Linux 7.1 using:
· linux 2.4.10
· gcc 2.95.3
· glibc 2.2.4 (libc.so.6)
· autoconf 2.52

and on Windows 98 using:
· MSVC 6.0

Versions of the code have also been built successfully on:
· MacOS X 10.3.9
· FreeBSD on Intel hardware
· Linux on Alpha hardware (Debian 2.2)
· Linux on Sparc hardware
· Linux on RS6000 PPC hardware
· Solaris 8 using gcc on Sparc hardware
· Solaris 8 using WorkShop 5.0
· Linux using intel c++ 6.0
· Windows NT 4.0 using MSVC 6.0
· Windows NT 4.0 using Cygwin (DLL 1.3.22) and gcc 3.2
· Windows NT 4.0 using MinGW 2.0.0 and gcc 3.2
· Windows XP using MinGW 3.1.0 gcc 3.4.2

What's New in This Release:

· Speed optimisations (as identified by KCachegrind/valgrind in KDevelop).
· Build-time size optimisations (eg. "./configure --disable-exec --enable-small-exceptions ...").
· Build-time options to reduce runtime library dependencies (eg. "./configure --disable-dns --disable-identity").
· New switch to limit the size of submitted messages ("--size").
· New semantics for "--poll 0", providing a good alternative to "--immediate" when proxying.
· SMTP client protocol emits a RSET after a rejected recipient as a workround for broken server protocols.
· SMTP client protocol continues if the server advertises AUTH but the client has no authentication secrets.
· When a message cannot be forwarded the offending SMTP protocol response number, if any, is put in the envelope file.
· A warning is printed if logging is requested but both stderr and syslog are disabled.
· A cross-compiling toolchain builder script added for running on mips-based routers ("extra/mips").
· New example scripts for SMTP multicasting and editing envelope files.
· Improved native support for Mac OS X (10.5) with graphical installation from disk image.
· Compatibility with gcc 2.95 restored.
Last updated on April 17th, 2008

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E-MailRelay is a simple SMTP proxy and relay MTA, written in C++, for Linux and Windows.


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