Am 12.02.26 um 10:03 schrieb Stefano Bagnara via mailop:
Hi all,
I didn't read news about it, but I see bogus "550 Invalid domain" replies to MAIL FROM from many IP/domains when
sending email to libero.it <http://libero.it> since 11/2/2026 16:00 CET (the transaction hangs some seconds in the
mail from and then returns the invalid domain error).
I confirmed the issue also sending from a consumer gmail inbox: I got a bounce "550
Invalid domain".
They probably have DNS issues and incorrectly configured SMTP handling of DNS failures. Any failures (except for
explicit NXDOMAIN responses) should IMHO lead to temporary rejections (4xx codes), not permanent rejections such as 550.
As we don't have much interaction with italian contacts, I did not see that
error on our mail systems.
Cheers,
Hans-Martin
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