451 4.7.500 Server busy. Please try again later

Question

Hi

We have a dedicated mail server (not Microsoft/Exchange) which has issues sending mails to our b2b-customers which uses a Microsoft service for their mail accounts (outlook.com).

Since yesterday all mails are throtteld (log entry anonymized):

Fehler: 451 4.7.500 Server busy. Please try again later from [...]. (S77719) [BE0DEU01FT009.eop-deu01.prod.protection.outlook.com 2023-10-11T13:06:02.927Z 08DBCA4DB698527E]

This happens to different mail-domains which are running through outlook.com.

Things we tried:

• joined SNDS - everything seems to be good with the ip and amount of mails
• sender/server IP is not blocked in Anti-Spam database - just throtteld
• filled out form "Sender Information for Outlook.com Delivery"
• tried to login to Login the Portal for a mail trace but our live account is not allowd to login in

We did not change anything in the mail server settings.

What can we do now?

Answer 1

Hi @Mareen Eisenmann ,

Welcome to our forum!

Looks like your issue is related to the transient known issue: Some users may encounter delays receiving external email messages in Exchange Online.

Microsoft has noticed this and is focusing on it. If you are the administrator, you can search EX680695 in the Dashboard and check the latest update of the issue.

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Answer 2

I have the same problem, this issue is not resolved !!