Why do I get this: 452 4.5.3 Recipients belong to multiple regions ATTR38

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Why do I get this: 452 4.5.3 Recipients belong to multiple regions ATTR38

Anonymous

Hi,

I moderate a mailing list of some 100 gmail, private and various Microsoft hosted addresses. When the list sends out a message there are 5 addresses that respond with this message. They are all hotmail addresses, none of the others do this. The full message is:

host hotmail-com.olc.protection.outlook.com [104.47.4.33]
    SMTP error from remote mail server after RCPT TO:<******@hotmail.com>:
    452 4.5.3 Recipients belong to multiple regions ATTR38 [AM5EUR02FT030.eop-EUR02.prod.protection.outlook.com]:
    retry timeout exceeded

These addresses are a subset of the microsoft addresses, they aren't even all the hotmail addresses on the list.

One of the addresses is my own test address, that has never marked anything as spam, and only receives email from this address. Also the mailing list is whitelisted in my test mail account. So it isn't (only) that the user has bounced previous mails from this source.

The most recent email is a very simple text only email.

I have DMARC and DKIM set up. Prior to this Gmail used to bounce as well. But for the last ~12 months only these hotmail addresses have bounced.

Thanks

Crispy

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Answer 1

452 4.5.3 Recipients belong to multiple regions ATTR38 [AM5EUR02FT030.eop-EUR02.prod.protection.outlook.com]:
    retry timeout exceeded

You're not the only one facing this problem. SMTP return codes starting with 4 (in this case 452) are temporary errors, which the server should attempt to deal with by retrying later. Apparently, if a message is addressed to multiple Outlook.com users in more than one region, it is delivered (other things being equal, of course) to those in the first region, but delayed to the remainder. (I'm not sure what 'region' means in this context, but my first guess would be the Azure region of the reporting MTA, which in the quoted case is EUR02.) The retry for the second region should follow immediately, but that for subsequent regions seems to fail with a timeout. The only authoritative reference I've found is this one, from Michael Wise of the Spam Analysis section at Microsoft at https://www.mail-archive.com/******@mailop.org/msg05411.html

From: Michael Wise [mailto:michael.w... @microsoft.com]

Sent: Thursday, 25 January 2018 6:33 AM

...

Subject: RE: Issues delivering to Hotmail addresses

Much internal discussion, but ...

Apparently ...

"452 is a special error code (per RFC) that instructs the sending MTA to retry the rejected recipients immediately.

"It is designed to split messages with a large number of recipients."

Apparently that's not exactly what we're using it for, but there you go. In theory, one or more of the recipients would deliver, and the first one to a different region would get this response, and then the next try for the remaining ... should deliver.

A fault at the Outlook.com end, then. Could you as an experiment split the list so that its parts only contain contain Outlook.com addressees in not more than two regions? You'd have to examine the NDRs to find the regions involved. The alternative would seem to be to resend the message to failed recipients individually or in regional groups.

You might try asking Michael for advice - I'm sure you can work out his email address from the munged one above.

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Why do I get this: 452 4.5.3 Recipients belong to multiple regions ATTR38

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