On Mon, Jan 26, 2026 at 09:15:00AM +0100, Benoit Panizzon via mailop wrote:
> Am Fri, 23 Jan 2026 22:51:47 +0000
> schrieb Michael Wise via mailop <[email protected]>:
>
> > S3150 == throttling, possibly daily limit.
>
> Nope, we got HARD 571 rejects stating the IP is on a blocklist.
I share that view of Benoit.
Here a small sample from one of our mailservers.
Col A: Mails to microsoft (certificate CN=mail.protection.outlook.com)
Col B: All of those rejected with S3150, SMTP 550 5.7.1
Col C: Relation of rejected to delivered mails (B/A).
Date A B C
20260106 706 99 14,02 %
20260107 2503 1 0,04 %
20260108 2432 85 3,50 %
20260109 1738 322 18,53 %
When I look at the logs, I find rejected and delivered emails within a few
minutes of each other. Therefore, I assume that the content of the email is
decisive for the blocking.
However, the fact that we had 10 days of the last 14 days with no S3150 at all,
speaks against this.
Looks more like we're lab rats in an AI experiment :-/
--
Greets
Frank
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