Fix SMTP Error 451 (Temporary local problem - please try later)

A problem that many face administratorand servers at the moment, it's due to a less common error SMTP which appears when sending an e-mail message. Fixed SMTP Error 451.

The causes of this error can be multiple, so it is good to investigate all possible causes in turn. In my case, in the first part of the tutorial I refer to a particular case.

SMTP Error 451 (Temporary local problem – please try later)

It's not about hacking or a problem caused by a configuration error. error SMTP 451 occurs especially on operating systems CentOS cu VestaCP installed, and the error log looks like this:

2020-07-03 11:17:11 Tainted filename for search: '/etc/exim/domains/domain.com/aliases'
2020-07-03 11:17:11 H=(costa.onlymale.live) [104.140.84.7] F=<15304-3132-5583-4006-name=domain.com@mail.onlymale.live> temporarily rejected RCPT <name@domain.com>: failed to expand "${extract{1}{:}{${lookup{$local_part@$domain}lsearch{/etc/exim/domains/$domain/aliases}}}}": NULL

I don't know if the problem is also for the servers that have them cPanel, but on VestaCP sure it's a problem. Virtually no user can send emails, even if the connection to the mail server seemed to be fine.

The error occurs as a result of a configuration incompatibilities in the most recent update by EXIM for CentOS (exim 4.94-1.el7), and until this moment there is no "fix" to solve this problem. However, there is a very simple solution.

How to solve SMTP error 451 (Temporary local problem - please try later)

Returning to the previous version of EXIM (downgrade) is the most convenient solution for administrators of mail servers with VestaCP.

1. We authenticate on Linux via SSH and execute the command lines through which we download and install the old version of EXIM.

wget https://stealthsettings.com/download/exim-4.93-3.el7.x86_64.rpm
rpm -Uvh --oldpackage exim-4.93-3.el7.x86_64.rpm

Output:

2. Restart "exim” and attention that the services “clamd"And"spamassassin" to run.

What I presented above is a particular case, but this type of error can be generated by various temporary causes that you must take into account and that you must investigate. Like, a problem with the recipient's email server exceeding the limit of sent messages in a time interval.

Other causes from which SMTP Error 451 may be present

→ SMTP error 451 can also indicate that the user has exceeded the limits set on the email server for sending emails. The e-mail server will not allow the user to send more e-mails than the established limits. These limits are set as daily or hourly limits to restrict abusive user behavior.

→ The recipient's e-mail server is overloaded with messages or has performance problems. It has a very high load and cannot process entry requests;

→ The recipient's e-mail server is undergoing maintenance. It is very possible that specific services and/or connectivity will be stopped;

→ There is a temporary problem with the network or with the connection to the recipient's e-mail server.