451 4.7.500 Server busy. Please try again later

Question

451 4.7.500 Server busy. Please try again later

Mareen Eisenmann 25

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?

Perger Balázs 5 Reputation points

2023-10-11T14:15:27.32+00:00

FYI https://learn.microsoft.com/en-us/answers/questions/1388575/e-mail-sending-to-offcie-microsoft365-customers-no
Sherif AboulGadayel 0 Reputation points

2023-10-11T18:18:11.59+00:00

I have the same problem. Can't send from company mail server to domains hosted at Outlook
Mareen Eisenmann 25 Reputation points

2023-10-11T18:40:32.9433333+00:00

follow the link
Lata 0 Reputation points

2023-10-12T16:38:05.2066667+00:00

Even we are still affected form India Region, mails to Microsoft 365 domains are not getting delivered.

Please whitelist IP 174.141.238.102 / 174.141.238.103

Accepted answer

1 additional answer

Your answer

Perger Balázs 5 Reputation points

2023-10-11T14:15:27.32+00:00

FYI https://learn.microsoft.com/en-us/answers/questions/1388575/e-mail-sending-to-offcie-microsoft365-customers-no
Sherif AboulGadayel 0 Reputation points

2023-10-11T18:18:11.59+00:00

I have the same problem. Can't send from company mail server to domains hosted at Outlook
Mareen Eisenmann 25 Reputation points

2023-10-11T18:40:32.9433333+00:00

follow the link
Lata 0 Reputation points

2023-10-12T16:38:05.2066667+00:00

Even we are still affected form India Region, mails to Microsoft 365 domains are not getting delivered.

Please whitelist IP 174.141.238.102 / 174.141.238.103

Answer 1

ChristyZhang-MSFT 26,126 Microsoft External Staff

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.

User's image

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.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Valentin Poddubnyak 0 Reputation points

2023-11-28T19:51:20.0333333+00:00

Nov 28 similar problems with some diffеrents domains under Microsoft:
451 4.7.500 Server busy. Please try again later from [x.x.x.x]. (S77719)

And Nov 29 working ok, thanks.

Damacio Martins 0

same problem 05/2024
host ativo-com.mail.protection.outlook.com[52.101.9.2] said:

451 4.7.500 Server busy. Please try again later from [x.x.x.x].

(S77719) [MN1PEPF0000ECDA.namprd02.prod.outlook.com

2024-05-09T20:05:44.372Z 08DC6DF434DB2B15] (in reply to end of DATA

command)

Damacio Martins 0 Reputation points

2024-05-09T20:51:20.9633333+00:00

please could you white list ip 5.161.72.245

Answer 2

Linh Phan 0

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

Screenshot from 2023-11-07 14-52-26

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451 4.7.500 Server busy. Please try again later

1 additional answer

Your answer