Our server hosts various domains, half of them using Google Apps for their e-mail and the other half simply does not use any domain e-mail accounts. However, the websites and applications (eg crons, firewall) on the server need to send out mail. For this purpose postfix was installed (Ubuntu 10.04). All works well.
However, analyzing the logs I see that there are a lot of failed incoming e-mails. Mainly because those domains that have no mail at this moment, still have some spam messages being sent to their domain. And as the DNS points to this server, they still show up here, taking up resources and clogging the log. So a few questions:
- Can I simply change the DNS and remove the MX entries? I am rather afraid that the OUTGOING mails will more often fail, as external spam filters check for valid MX entries and see that these domains are not even supposed to send out mail. (I still want them to read @domain.com when sending it out). Or should a SPF record solve this problem?
- Should I replace Postfix with something lighter/better equipped for just sending mail? All incoming mail software is currently unused.
- Is there another way to make postfix outgoing-only, and avoid all of these log-entries?