Some emails may be delayed by your server or may be rejected by the server. Analysis of this error on Plesk Linux servers; let’s do,
First of all, from a service provider (Hotmail is preferable.) Let us a mail to the address in a domain located on our Plesk Linux server, then connect with ssh,
tail -1000 /usr/local/PSA/var/log/maillog | grep [email protected]
Let’s see the error returned with the command;
milter-reject: DATA from mail-oln040092066039.outbound.protection.outlook.com[18.104.22.168]: 451 4.7.1 Service unavailable – try again later; from =<[email protected]> to=<[email protected]> proto=ESMTP helo=<EUR01-VE1-obe.outbound.protection.outlook.com>
We have seen the error; this error is caused by the crash of the Plesk milter service, let’s fix and disable it via postfix;
grep milters /etc/postfix/main.cf
smtpd_milters = ,, inet:127.0.0.1:12768 unix:/var/spool/postfix/ctmilter/ctmilter.sock non_smtpd_milters = ,, inet:127.0.0.1:12768 unix:/var/spool/postfix/ctmilter/ctmilter.sock
The configuration lines are available in main.cf, in two lines, we need to remove them,
Open our postfix main configuration file and search with ctrl + w and search for and remove the smtpd_milters and non_smptd_milters lines.
Let’s re-install and test our configuration; you will see that it was improved.