At one of our client sites, we experienced a strange behaviour where incoming emails were being rejected for policy reasons and outgoing emails were not being delivered.

04/15/2009 01:34:40 PM  Router: Failed to connect to SMTP host HOST.SOMEDOMAIN.COM because The server is not responding. The server may be down or you may be experiencing network problems. Contact your system administrator if this problem persists.

Or something like this : Mail from user@somedomain.com rejected for policy reasons. Domain not found in DNS.

The quick solution was to have “tell router update config” command run every 30 minutes (less is better) so that domino can flush its DNS record that have been cached. Strange behaviour as we have to do it often.

Here is the screen shot

**Update 4/20/2009**

We requested a PMR from IBM and it may turn out that there could be a problem in the Domino code itself. The support engineer has escalated this issue for a possible hotfix. We experienced this issue using Domino 8.0.2 FP1 plus another server that runs on Linux with Domino 8.5 has also had a similar problem, but mails for some reason get delivered after a couple of seconds on the 8.5 server.

IBM has provided us with a hotfix to solve the problem where Domino server caches an A record until 2043 when an MX record is not found during DNS query or when there is an error. In case you are interested, the hotfix number is 287 (02FP1HF287) but I believe you have to get it by calling in to IBM support. Here is a quote from the support engineer :

It sets a default TTL for DNS that router uses in its cache to 30 minutes when an error occurs or when a non-MX record is returned.

This default is adjustable by the INI RouterDNSErrorTTL. The INI expects seconds so a value of 3600 would be 1 hour. I would not recommend adjusting the TTL unless needed so do not use the INI unless there is a reason.

 To get more detail on your log and to see whether it caches certain A record until year 2043, increase the debug output level by entering the following into the Domino console:

start consolelog
set config debug_threadid=1          (0 to disable)
set config debugrouter=3                 (0 to disable)
set config log_mailrouting=40       (20 to disable)
set config smtpclientdebug=3        (0 to disable)
restart task router