I returned to the desk now, and checked the log. It got sent with a delay of 20001 (seconds, that is).
What I wanted to say is: Our mailserver wanted to send a mail, the other mailserver tried to validate the address by probing our mailserver, but got caught in a "450 Greylisted", and afterwards denied our mail attempt as "450 Unverified address". And our retries to send the mail didn't trigger another probe by their server, but got rejected directly. If they would have tried to probe again, that would have been allowed by our greylisting.
Interesting part is now, the message got sent without any additional probing by their mail server, it was plainly accepted. It's possible to me that there is a postmaster at the other server who caught this problem in their logfile and either corrected their sender address verification or whitelisted our sender address.
Thanks to everyone who broke their head about the issue. |
