Plesk 451 4.7.1 Service unavailable – try again later

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[]: 451 4.7.1 Service unavailable – try again later; from =<[email protected]> to=<[email protected]> proto=ESMTP helo=<>

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/

Let’s see,

smtpd_milters = ,, inet: unix:/var/spool/postfix/ctmilter/ctmilter.sock non_smtpd_milters = ,, inet: unix:/var/spool/postfix/ctmilter/ctmilter.sock

The configuration lines are available in, in two lines, we need to remove them,

nano /etc/postfix/

Open our postfix main configuration file and search with ctrl + w and search for and remove the smtpd_milters and non_smptd_milters lines.

After that;

postfix reload

Let’s re-install and test our configuration; you will see that it was improved.

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