Does anyone know what the root cause of messages like the following are? Are there ways to mitigate these problems?

Final-Recipient: rfc822;[email protected]
Action: delayed
Status: 4.4.7
Diagnostic-Code: smtp;400 4.4.7 Message delayed
Will-Retry-Until: Thu, 11 Feb 2010 08:21:49 +0000
X-Display-Name: First Last

4 Answers 4



It is a common misconception that email delivery is instantly completed. Email is designed to be sent from Mail Server to Mail Server until it reaches the ultimate destination with no guarantee on how long it will reside at each intermediary stop. Most cases of delayed email are due to slow or overloaded mail servers. Email delivery delays are caused by spam, frequency of checking one's email, or other hardware issues. When an email is delayed for a significant amount of time, the best way to check why an email is delayed is to analyze the email header on the delivery delay notification to see where the delay is occurring.

It's also likely that it was intentionally delayed: http://www.byui.edu/help/outlookhelp/mailing/delayed.htm

  • @Sathya: I wish I could upvote an edit. Thanks!
    – valbaca
    Commented Feb 21, 2014 at 1:10
  • Note that the second link is dead.
    – normanius
    Commented Aug 13, 2020 at 10:09

I don't know about today, because I'm not in that loop anymore, but, when I was working for an ISP, I was very aware of the eMail parameters. It was not unusual for a normal eMail to be delayed by 15 minutes to a half hour because of the way that eMail is passed on the net. The primary reason for this is the individual ISP eMail parameters. I was working for a small ISP who was limited to sending eMail every 15 minutes. The timer that batched off the eMail was set to a minute that was not one of the primary quarter hours. Each ISP along the line is doing the same thing, most more often (something like every 10 minutes or 5 minutes depending on the size of the ISP). Because of this the automatic delay for an eMail could range from immediate to as much as an hour with no other reason involved.


There could be many reasons for the email delay, the email headers include all information about the routing of mail check this how to http://www.knotrick.com/what-causes-email-to-delay/

  • While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes.
    – Andrea
    Commented Jan 23, 2014 at 8:21

It may be obvious to some but always check to be sure your antivirus/antimalware/antiexploit software isn't causing issues. I had a local smtp server configured to deliver through an office 365 account and malwarebytes was blocking any processing from happening in the mail queue folder. Once I whitelisted the inetpub directory my smtp server started working again.

  • The email server in this case isn't local from the context of the question.
    – Ramhound
    Commented Jun 22, 2015 at 18:40

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