Remote Server returned '550.4.4.7 Queue.Expired; message expired

Occasional Contributor

Hi All

One of my user( is not getting email from other domain user( my user is getting emails from other users of that domain except one user i.e Glenn. Glenn is getting the below NDR when he is sending email to my user. is it issue at my end or at other domain end. When i check at email gateway, i can see similar email with same subject from Glenn received by one of my other user on a different date. Below is the NDR which is Glenn is getting when sending to my user.

Delivery has failed to these recipients or groups.
The server has tried to deliver this message, without success and has stopped trying.
The recipient mail server may be temporarily offline or temporarily unable to accept message. 

Diagnostic information for administrators:
Generating server:
Total retry attemps:75
Remote Server returned '550.4.4.7 Queue.Expired; message expired.

1 Reply
best response confirmed by maxwell2k19 (Occasional Contributor)
issue seems to be at senders end, their exchange is not able to send emails out.
a good place to start would be to check if they are able to reach your servers at port 25.