pSome internet access providers have port 25 disabled in their routers to prevent spam. If you run your own email server in a data center, you might have to enable the submission port (587) in postfix to be able to send emails from your local email client to your own mail server. Enable Submission Port ... Read more
More and more internet access providers are closing port 25 to reduce spam except for connections to their own mail servers. If you run your own email server and have problems connecting to it on port 25, you can enable port 465 (SMTPS) in postfix as a workaround. Edit the /etc/postfix/master.cf file: nano /etc/postfix/master.cf and ... Read more
Postfix provides several shell programs to manage the mail queue. These are: postsuper postqueue mailq In this tutorial, I will show you how to use these commands to manage the Postfix mail queue. Here are examples for common tasks: List all messages that are in the mail queue postqueue -p The output looks like this: ... Read more
If you get an error like: Apr 15 12:41:03 webb4 postfix/sendmail[11234]: fatal: web1_user(12967): queue file write error in your mail log, then the value for message_size_limit in postfix main.cf is too low. Solve Postfix queue file write error Edit postfix main.cf: nano /etc/postfix/main.cf and set the message size limit to a higher value. E.g. message_size_limit ... Read more
When a server has more than one IP address, then postfix will use all IP addresses randomly to send out emails. This can cause your emails to be listed as SPAM on other servers because the sending IP does not match the reverse IP of the server hostname. The solution is to bind postfix to ... Read more
The command below enables a stricter SPAM handling for postfix on ISPConfig 3 servers. In Detail: Reject sender hostnames with invalid syntax Reject sender hostnames that are no fully qualified domains (e.g. reject "server1" but allow server1.domain.tld) Reject sender domains that have no DNS records Check sender IP addresses against realtime blacklists. First make a ... Read more
You might see the error: postfix/master[5309]: fatal: 0.0.0.0:smtps: Servname not supported for ai_socktype On a OpenSuSE server when you enable smtps in postfix master.cf file. The reason for the error is that the definition of the smtps port in /etc/services is missing. Solution Edit the /etc/services file vi /etc/services and add the following lines: smtps ... Read more