A mail was delivered through a forward, with the final location at a company email server. During this delivery there was a pretty long delay, and it looks like the delay is the result of SPF (Sender Policy Framework) fail as seen in spf=fail below:

Received: from [...]; Fri, 16 Sep 2016 09:47:57 +0200

Authentication-Results: ppops.net;
    spf=fail smtp.mailfrom=[...]@[...].com;

Received: from [...]; Thu, 15 Sep 2016 21:30:34 +0200

What is the reason for the delay, and why was the mail accepted and delivered after all ?

  • It also depends on the policy statement. Check host -t any domain.com to see the SFP record, there are options like +all, -all, ~all, ?all. – Aria Sep 16 '16 at 9:15

What is the reason for the delay, and why was the mail accepted and delivered after all ?

It is impossible to tell what has caused the delay since we have no information what software is running on the receiving and sending server, have no access to the log files etc.

One reason for the delay might be Greylisting where mail from yet unknown senders/recipient combinations gets temporary rejected in the hope that a good sender will retry later while a bad sender (spam) will just give up because retrying is too costly. But usually the delay is not that long as in your mail, i.e. maybe 15..60 minutes only.

Of course it can simply be that the server was not reachable, the mailbox was full or similar problems. I very much doubt that this has anything to do with the SPF record because an SPF fail might cause a mail not not be delivered at all but not to be just delivered some hours later.

  • The delay is not due to mail box full, and I doubt also unreachable server. – Morten Zilmer Sep 16 '16 at 10:06
  • @MortenZilmer: these were just examples. It might also be that one of the MTA was down, internet down, recipient MTA disk full ... - again: it is impossible to say just from this mail and without having access to the related logs at the servers. Everything one can do is intelligent speculation. – Steffen Ullrich Sep 16 '16 at 10:08
  • Thanks for the suggestions, and it helps me to know what to look for :-) – Morten Zilmer Sep 16 '16 at 10:10

It's a matter of what type of defense they use. In this case, published and checked SPF records have instant priority and the others will be queued at a specific interval, so there will be delays in delivering them. Some RBL filters also use this tactic: you will have delays if you're not white-listed and you send a higher-than-the-stats volume of e-mails.

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