Is there a secure feature in outlook that automatically sets the maximum recipients to 1?

SungBin Hong 20 Reputation points
2023-11-21T05:25:18.68+00:00

Thank u for your kind answer. (https://video2.skills-academy.com/en-us/answers/questions/1427741/how-to-send-email-having-more-than-one-receiver-to)

But, i have one more question about it.

You mean, basic implementation of your smtp server keeps the RFC 5321 document. This case ("Too many recipients (AS780090)") is related with their own security policy. For example, recipient limits.

Actually, i checked that i can append more than one user with 'outlook-com.olc.protection.outlook.com' server. (i got this server domain with 'nslookup outlook.com')

User's image

There is one last thing I want to check.

I always encounter "Too many recipients (AS780090)" message when i try to request more than one RCPT_TO command with '{user-domain}.mail.protection.outlook.com'.

So.. in this case, all organizations set the max recipients as 1. But this is something weird.
Is there a secure feature in outlook that automatically sets the maximum recipients to 1?

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  1. Kael Yao-MSFT 37,666 Reputation points Microsoft Vendor
    2023-11-21T05:56:07.0633333+00:00

    Hi @SungBin Hong

    To my knowledge this may be caused the ip address you are sending from is being throttled by Exchange Online Protection.

    If you have access to Microsoft 365 admin center, please create a service request to contact Microsoft 365 (Exchange Online) support to have them check if they can whitelist your ip address.

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