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MTA 'deferred' queue builds up and does not release emails Technical Level
Symptoms
  • Emails are accumulating in the MTA "deferred" queue.
  • Postfix queue shows many emails with this message:
    [Expert@HostName:0]# /opt/postfix/usr/sbin/postqueue -c /opt/postfix/etc/postfix/ -p

    4HfWQQ6gfZzD5c9 79716 Wed Oct 27 10:31:21 bounce@domain.com (host 10.1.1.30[10.1.1.30] said: 452 4.3.1 Insufficient system resources (SystemMemory) (in reply to end of DATA command)) user@domain2.com
Cause

Next Hop IP, which is usually an email server, sent this error: "452 4.3.1 Insufficient system resources (SystemMemory)".


Solution
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