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Debian GNU/Linux Reference Guide
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9.6.1 Mail transport agents (MTAs)

For a full-featured MTA, use exim in Woody and use exim4 in Sarge. [ 44] References:

  • exim-doc and exim-doc-html packages for exim

  • exim4-doc-info and exim4-doc-html packages for exim4

  • https://www.exim.org/

The only reasonable alternative MTA is postfix if you care about security. sendmail and qmail are available as Debian packages but are not recommended.

If you do not need the relay capability of an MTA as in the case of a satellite system such as a laptop PC, you may consider using one of these lightweight packages:

  • ssmtp: needs an SMTP connection and is alias-capable, or

  • nullmailer: can spool but is not alias-capable.

At this moment, I find exim to be more suitable even for my personal workstation machine, which is a laptop PC.

You may need to remove exim for the installation of these conflicting packages:

     # dpkg -P --force-depends exim
     # apt-get install nullmailer         # or ssmtp

9.6.1.1 Smarthost

If you are running exim4 or exim on a host which is connected through the consumer grade services, please make sure to send outgoing mail through a smarthost offered by your ISP or some others. [45] There are few good reasons:

  • to ensure SMTP retries since your ISP's smarthost usually have more reliably connection.

  • to avoid sending mail directly from a dynamic IP address which will likely be blocked by dial-up spam lists.

  • to save your local bandwidth to send mails with multiple recipients.

The only conceivable exceptions are:

  • the emergency cure for your ISP's SMTP service trouble.

  • an experiment for the educational purpose.

  • your host being a professionally hosted server.


9.6.1.2 Basic configuration of Exim

In order to use exim4 or exim as your MTA, configure the following:

     /etc/exim/exim.conf     "eximconfig" to create and edit (exim)
     /etc/exim4/*            "dpkg-reconfigure exim4-config" to create and edit (exim4)
     /etc/inetd.conf         comment out smtp to run exim as daemon
     /etc/email-addresses    Add spoofed source address lists

check filters using exim4 or exim with -brw, -bf, -bF, -bV, ... etc.


9.6.1.3 Setting up a catchall for nonexistent email addresses under Exim

In /etc/exim/exim.conf (Woody or later), in the DIRECTORS part, at the end (after the localuser: director) add a catch-all director that matches all addresses that the previous directors couldn't resolve (per Miquel van Smoorenburg):

     catchall:
       driver = smartuser
         new_address = [email protected]

If one wants to have more a detailed recipe for each virtual domain, etc., add the following at the end of /etc/exim/exim.conf (per me, not well tested):

     *@yourdomain.com ${lookup{$1}lsearch*{/etc/email-addresses} \
             {$value}fail} T

Then have an "*" entry in /etc/email-addresses.


9.6.1.4 Configuring selective address rewriting for outgoing mail under Exim

Selective address rewrite for outgoing mail to produce proper "From:" headers can be done using exim by configuring near the end of /etc/exim/exim.conf:

     *@host1.something.dyndns.org \
       "${if eq {${lookup{$1}lsearch{/etc/passwd}{1}{0}}} {1}  \
        {$0}{[email protected]}}"  frFs

This rewrites all addresses matching *@host1.something.dyndns.org.

  1. It searches through /etc/password to see if the local part ($1) is a local user or not.

  1. If it is a local user, it rewrites the address to the same thing it was in the first place ($0).

  1. If it is not a local user, it rewrites the domain part.


9.6.1.5 Configuring SMTP authentication under Exim

Some SMTP services such as yahoo.com require SMTP auth. Configure /etc/exim/exim.conf as follows:

     remote_smtp:
       driver = smtp
       authenticate_hosts = smtp.mail.yahoo.com
     ...
     
     smarthost:
       driver = domainlist
       transport = remote_smtp
       route_list = "* smtp.mail.yahoo.com bydns_a"
     ...
     
     plain:
       driver = plaintext
       public_name = PLAIN
       client_send = "^cmatheson3^this_is_my_password"

Do not forget double quotes in the last line.


Debian GNU/Linux Reference Guide
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