Error: 550 5.4.300 Message expired -> 451 Temporary local problem - please try later

New Contributor



Since moving a specific domain to Office365 mails going out to a few domains always end up being returning with the above error 451 Temporary local problem.


Then after a while the I see from the Exchange Admin center, mail flow - there was a error and then later a successful delivery.


The domain is not listed anywhere as spam, and the recipients have also white-listed the domain.

Here is an example;


Reason: [{LED=451 Temporary local problem - please try later};{MSG=};{};{IP=};{LRT=8/25/2020 8:02:56 AM}]. OutboundProxyTargetIP: OutboundProxyTargetHostName:


Reason: [{LED=550 5.4.300 Message expired -> 451 Temporary local problem - please try later};{MSG=};{};{IP=};{LRT=8/26/2020 7:22:49 AM}]. OutboundProxyTargetIP: OutboundProxyTargetHostName:

2 Replies
best response confirmed by lava_za (New Contributor)

This looks like a case of graylisting… best work with the other side to add an exception for your domain or similar.

@Vasil Michev Thank you kindly for the reply, your suspicion was correct as the recipient mail server filtering had a static IP bound to the sender that was the old MX records, and hence it was permanently placing the sender in a grey-list. 

Solved by requesting a removal.