Common Problems

The following error messages in the mail log files indicate host lookup problems:

mail for domain loops back to myself

This is one of the most common errors related to DNS. It happens when you have configured your Postfix server as an MX host in your DNS server, but you have not told your Postfix server that it is the final destination for the domain. Add the domain in question to the mydestination parameter, or configure it as a virtual domain or a relay domain. If your Postfix server is behind a proxy or NAT device, it may not realize that it is an MX host for the domain. In that case, add the proxy device's IP address to proxy_interfaces. Log entries for this error resemble the following:

postfix/qmgr[3981]: 2CC3B229: from=, 
 size=306, nrcpt=1 (queue active)
postfix/smtp[3983]: warning: mailer loop: best MX host for 
 example.com is local
postfix/smtp[3983]: 2CC3B229: to=, 
 relay=none, delay=0, status=bounced (mail for example.com 
 loops back to myself)

Host found but no data record of requested type

The domain's DNS configuration has no MX records and there is no A record for the domain itself. You will have to contact an administrator of the domain to fix the problem. For your own domains, be sure they all include MX records pointing to your mail server. Log entries for this error resemble the following:

postfix/qmgr[3818]: D31CD20F: from=, 
 size=312, nrcpt=1 (queue active)
postfix/smtp[3824]: D31CD20F: to=, 
 relay=none, delay=1, status=bounced (Name service 
 error forname=example.com type=A: Host found but 
 no data record of requested type)

no MX host for domain has a valid A record

The domain's DNS configuration has MX records, but lookups for the IP addresses fail. You will have to contact an administrator of the domain to fix the problem. For your own domains, be sure that any hosts you specify as MX hosts are valid and have correct A records. Log entries for this error resemble the following:

postfix/qmgr[3818]: 068DB20F: from= 
 size=306, nrcpt=1 (queue active)
postfix/smtp[3846]: warning: no MX host for example.com has 
 a valid A record
postfix/smtp[3846]: 068DB20F: to= 
 relay=none, delay=1, status=deferred (Name service 
 error for name=mail.seaglass.com type=A: Host not found)

Host not found, try again

The DNS query produced no answer. Either the DNS server is not reachable, or it is broken. Assuming the DNS server for this domain is up and working correctly, this error message could be due to a networking problem, or perhaps your system's resolver is misconfigured. Check over the documentation for the nsswitch.conf and resolv.conf files on your platform. Be sure that your system is resolving DNS queries correctly, using one of the tools mentioned earlier in the chapter, before trying to troubleshoot the problem with Postfix. Log entries for this error resemble the following:

postfix/qmgr[3818]: CCBED1E8: from= 
 size=306, nrcpt=1 (queue active)
postfix/smtp[3937]: CCBED1E8: to= 
 relay=none, delay=1, status=deferred (Name service error 
 for name=example.com type=MX: Host not found, try again)

If you are running Postfix in a chrooted environment, there are several configuration files related to DNS that must be within the chrooted compartment. See Chapter 4 for more information on running Postfix within a chroot.