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-----
ESMTP
-----
José Fonseca
---
July 2003
Introduction
~~~~~~~~~~~~
<<esmtp>> is a user configurable relay-only Mail Transfer Agent (MTA) with a
<<sendmail>> compatible syntax. It's based on <<libESMTP>> supporting the
AUTH (including the CRAM-MD5 and NTLM SASL mechanisms) and the StartTLS SMTP
extensions.
See the {{{http://esmtp.sourceforge.net/}ESMTP home page}} for updated
information.
Configuration
~~~~~~~~~~~~~
* Sample configuration files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is a simple configuration file for a quick start:
--------------------------------------
hostname = mail.myisp.com:25
username = "myself"
password = "secret"
starttls = enabled
mda "/usr/bin/procmail -d %T"
--------------------------------------
If you have more than one SMTP account you have them automatically chosen for
you:
--------------------------------------
identity myself@myisp.com
hostname mail.myisp.com:25
username "myself"
password "secret"
starttls enabled
default
identity myself@anotherisp.com
hostname smtp.anotherisp.com:25
username "myself"
password "secret"
mda "/usr/bin/procmail -d %T"
--------------------------------------
* Configuration options
~~~~~~~~~~~~~~~~~~~~~~~
See the <<esmtprc>> man page for more detailed information on the
configuration options.
Invocation
~~~~~~~~~~
<<esmtp>> is command line compatible with <<sendmail>>.
See the <<esmtp>> man page for information on how to invoke it.
Interfacing to Mail User Agents
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Most Mail User Agents (MUAs) will work without need to configuration provided
that you install a symbolic from <<</usr/sbin/sendmail>>> to the esmtp
executable. This should already be taken care of by the <install> target of
the makefile when building from source.
If by any reason it is not possible to have (such as no administrator
privileges or the use of another MTA for local delivery) then you will have
to reconfigure your MUA to use the esmtp executable instead.
* Mutt
~~~~~~
If not using a symbolic link to the esmtp executable you can make <<Mutt>> use
<<esmtp>> by adding the following line to your <<<~/.muttrc>>>:
-----------------------------
set sendmail="/path/to/esmtp"
-----------------------------
<<Esmtp>> supports <<sendmail>> envelope sender <-f> flag, and you are
advised to always enable it by adding the following line to <<Mutt>>
configuration file:
---------------------
set envelope_from=yes
---------------------
For debugging purposes you may prefer to put in your <<<~/.muttrc>>>:
--------------------------------------------------
set sendmail="/path/to/esmtp -v -X /tmp/esmtp.log"
--------------------------------------------------
This will enable verbose output and logging of the traffic with the SMTP
server.
Interfacing to Mail Delivery Agents
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<<esmtp>> relies upon a Mail Delivery Agent (MDA) for local mail delivery, so
you need one if you want to avoid having another MTA for local delivery.
Notice that at the moment <<esmtp>> does not honor mail aliases or
<<<.forward>>> files.
To deliver to other users beside yourself, the MDA must be installed with
<setuid> flag -- which is done by default in most Linux distributions.
* Procmail
~~~~~~~~~~
To use <<procmail>> with <<esmtp>> set the <<<mda>>> configuration value to:
-----------------------------
mda="/usr/bin/procmail -d %T"
-----------------------------
If the mail message doesn't have a Date: header, such as those generated by
vixie-cron, neither <<esmtp>> or <<procmail>> will add one for you. A simple
hack is to pipe the message through the <<formail>> program (also part of the
<<procmail>> distribution), such as:
------------------------------------------------------------
mda='/usr/bin/formail -a "Date: `date -R`" | /usr/bin/procmail -d %T'
------------------------------------------------------------
Or, alternatively, add the following rule to your <<<.procmailrc>>>:
----------------------------------------------
:0fw
* ! ^Date:
| formail -a "Date: `date -R`"
------------------------------
Interfacing with other mail applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Fetchmail
~~~~~~~~~~~
By default <<fetchmail>> delivers messages via SMTP to port 25 on the machine
it is running. Because <<esmtp>> has no SMTP server if you are not using another
MTA for local delivery then you will need to configure <<fetchmail>> to use
<<esmtp>> executable. This is accomplished by adding the following lines to the top
of your <<<~/.fetchmailrc>>>:
-------------------------------------
defaults
mda "/path/to/esmtp -f %F %T"
-------------------------------------
Since <<esmtp>> simply forwards the mail to another MDA you can avoid this
redundant step by simply replacing the value inside the quotes above by
whichever value you use on your <<<~/.esmtprc>>>.
Using the StartTLS extension
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TLS support in <<libESMTP>> although usable is not yet as robust and
featureful as the rest of the library. At the moment to use the StarTLS
extension you will need to:
[[1]] create a ~/.authenticate directory for the certificates. All files
and directories in ~/.authenticate (including itself) must be user-readable
only , i.e., they must have 0600 and 0700 permissions respectively.
[[2]] put the certificate of the trusted Cert-Authority that signed the
server certificate into <<<~/.authenticate/ca.pem>>>.
[[3]] if a client certificate is required by the server then put it
(including the private key) into
<<<~/.authenticate/private/smtp-starttls.pem>>> or
<<<~/.authenticate/host.name/private/smtp-starttls.pem>>>. If your client
certificate has a passphrase then it should be specificied with the
<certificate_passphrase> configuration.
[[4]] enable (or require) the StartTLS extension with the <starttls>
configuration option. Note that the value of the <hostname> configuration
option of the server you connect MUST match the name in the server
certificate, since it will be used to verify the server identity.
In case of failure no error message will appear. Instead, <<libESMTP>> will
terminate the SMTP connection right after issuing the STARTLS command.
For more information about TLS support in <<libEMSTP>> see (here in
cronological order, and roughly in reverse-order of importance):
* {{http://mail.gnome.org/archives/balsa-list/2002-February/thread.html#00225}}
* {{http://mail.gnome.org/archives/balsa-list/2002-March/thread.html#00000}}
* {{http://mail.gnome.org/archives/balsa-list/2003-September/thread.html#00011}}
* {{http://mail.gnome.org/archives/balsa-list/2003-September/msg00023.html}}
* comments in smtp-tls.c in the <<libESMTP>> source distribution.
Also of interest may be:
* {{http://postfix.state-of-mind.de/patrick.koetter/smtpauth/postfix_tls_support.html}}
|
