When your sender got the bouce back email with the message
SMTP error from remote mail server after MAIL FROM: SIZE=5000000:
host mail.domain.com [xx.xx.xx.xx]: 552 Message size exceeds maximum permitted
Increase the message size limit set. Follow the steps given bellow.
1. Login to ypur server with the ssh access and root user
2. Edit exim.conf files.
3. Search for “message_size_limit” and change the limit.
message_size_limit = 6M
Note :: I used 6 megabytes in my example, you change change 5m to whichever size you would like.