The Exim 4 source code supports authentication with SASL since version 4.43. Debian started enabling this feature in exim4_4.50-2. After I’ve had upgraded to that version and replaced my saslauthd authenticators with brand-new cyrus_sasl authenticators, I’ve noticed that auth.log got flooded with entries like ‘exim4: OTP unavailable because can't read/write key database /etc/opiekeys: No such file or directory.’

My exim configuration uses three different cyrus_sasl authenticators and each exim invocation resulted in three of these OTP warnings because exim calls sasl_listmech() for each configured authenticator. It doesn’t specify a limiting mech_list, that means SASL will test which of all installed mechs actually can be used for authentication. Debian’s SASL package includes libotp.so, so it also tries to use OTP which is not configured on my system.

There are two ways to get rid off the warnings:

• Remove /usr/lib/sasl2/libotp.*. You’ll have to do this after each upgrade of the libsasl2-modules package.
• Rebuild exim with this patch. The patch specifies a limiting mech_list option for SASL. This limits sasl_listmech() to the mechs used in the exim configuration. Other mechs won’t be tried anymore.

May 3rd, 2005: A slightly modified version of the patch has been integrated into Exim CVS and will be included in the next Debian release of exim4 (see Debian bug #299743)

I’ve recently changed my network connection at home to a provider which assigns dynamic addresses. Exim always provided a broken HELO/EHLO name to my smarthost since then because my externally visible hostname changes each time I connect. I’m now using Exim’s Perl interface to lookup the assigned hostname when connecting my smarthost:

• /etc/exim4/exim.pl:
  Don’t forget to change ppp0 to the interface you want to handle!

  #! /usr/bin/perl
  
  # Requires libio-interface-perl
  
  use strict;
  use IO::Socket;
  use IO::Interface;
  
  sub get_remote_helo_data()
  {
      my $s = IO::Socket::INET->new(Proto => 'udp');
      my $addr = inet_aton($s->if_addr('ppp0'));
      my $hostname = gethostbyaddr($addr, AF_INET);
  
      $hostname = '' if (!$hostname);
  
      return $hostname;
  }
  

• /etc/exim4/conf.d/main/50_exim4-localconfig_perl:

  #main/50_exim4-localconfig_perl
  perl_at_start = true
  perl_startup = do '/etc/exim4/exim.pl'
  

• Add the following code to the appropriate transport, e.g. remote_smtp_smarthost:

  helo_data = \
    ${if >{${strlen:${perl{get_remote_helo_data}}}}{0} \
                   {${perl{get_remote_helo_data}}} \
                   {$primary_hostname}}