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On our mailing list, we have been getting the following message Maximum failsafe period has expired. What does that mean?

Mike Wills
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It probably refers to the retry cycle that most mail transfer agents use in the face of error conditions that may be temporary (i.e. "can not contact server" is potentially a temporary problem due to network/DNS issues but "user does not exist" is pretty much considered to be a permanent state for the purpose of the current message).

What usually happens in these cases is that the message is dropped back on the queue to retry sending in a few minutes. After a couple of retries the mail server will start retrying every hour instead of every few minutes. After a few more it will start retrying every 24 hours, and after a few days it will bounce the message back. The amount of retries, and the periods between them, is not a defined standard: different mail servers will use different timings.

So if I were to get the "Maximum failsafe period has expired" message in a reply/bounce then I would assume the destination mail server is inaccessible.

David Spillett
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  • Our mail server sends out "this couldn't be sent for the last 4 hours" as a bounce message. This happens almost immediately. Google searches haven't turned up anything for me. – Mike Wills Aug 14 '10 at 02:38
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    Is it just one server/domain that is sending this message back, or many. If just one then it could indicate a fault like the mail server's queue being full due to not being able to forward things on to the next stage - it could just be bad design that is sends the same message for two queue related issues (individual mail on the queue too long and queue not having room to put the mail on the queue in the first place). – David Spillett Aug 14 '10 at 10:04
  • Yes, just one domain. – Mike Wills Aug 19 '10 at 15:19
  • Can you tell anything about the mail server? If you telnet to port 25 on the domains mail servers it may tell you what it is, for instance mine announces itself as Postfix. That information may make tracking the meaning of the error down a little easier, though be aware that it is quite possible for the server to lie about itself in any such announcement. – David Spillett Aug 19 '10 at 20:22