unable to send email.

Question

Hi All

i am using exchange 2016 hybrid environment. we create users in onprem and migrate to online. An external user is trying to send email to one of my user(******@contoso.com). and the external user is getting the below error.

Your message to ******@contoso.com couldn't be delivered. When Office 365 tried to send your message, the receiving email server outside office 365 reported an error. Policy violation or system error.

Please guide me , is anything which needs to be checked at sender domain end or recipient Domain end.

Answer 1

Hi @Glenn Maxwell

1.If the attachment is too big, the line length of the header field is too long, so the receiving email server will reject the message.
2.Are there any email filtering or spam policies that may block emails from external senders? Check if the sender is in the recipient blacklist.

3.Check whether external users are able to send emails to other users in the organization.

Check whether the recipient user (******@contoso.com) is able to receive emails from other external senders.

Just to confirm if your problem is the same as this?
Does the error detail contain "Status code: 550 5.0.350"?

Regards

Shaofan

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