Internal error AUP#BL (in reply to end of DATA command)

As of a few days ago, we’re getting this in response to emails being sent to employee cellphones twice a day. Everything had been working fine for the last few years and we made no changes:

May 16 14:02:56 xxxxxx postfix/smtp[29154]: 5A958529F9B: to=<[email protected]>,[]:25, delay=601, delays=597/0.01/2.2/1.6, dsn=4.2.0, status=deferred (host[] said: 421 4.2.0 qf3XniGvu0Ngnqf3Xnt3Qf internal error AUP#BL (in reply to end of DATA command))

May 16 14:02:56 xxxxxx postfix/smtp[29153]: 5A958529F9B: to=<[email protected]>,[]:25, delay=601, delays=597/0.01/2.2/1.5, dsn=4.2.0, status=deferred (host[] said: 421 4.2.0 qf3XnL9yDRujdqf3XnkK0x internal error AUP#BL (in reply to end of DATA command))

This is only happening to email going to and according to our server’s logs. AUP#BL seems to me to mean “acceptable use policy # blocklist”, but that’s just my guess. We don’t use Cloudflare to handle our outgoing mail, so I’m not sure what’s going on here.

I have found our server provider listed on one blocklist at where they want money to whitelist our specific IP. Does Cloudflare use that blocklist, or can someone clue me in on what’s going on? I can’t find anything matching this on Google.

I believe I’ve found the problem. The email contains a link to a server function. Removing the link allows the email to go through. I’m not sure if this is Cloudflare intercepting things or TMobile and MetroPCS doing something. is not a service run by Cloudflare to my knowledge. They s sounds like an issue with your origin / mail provider

You are right. I totally misread that. It’s cloudfilter, whoever that is. I’ll get in touch with them, now that I know what their issue is.

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CloudFilter/Cloudmark/ProofPoint/whatever is likely being used by T-Mobile.