おはようございます ありがとう
backyつかってます
先方から今朝メールが送った分複数届いていると連絡がありました

This Message was undeliverable due to the following reason:
The user(s) account is temporarily over quota.
<[email protected]>
Please reply to <[email protected]>
if you feel this message to be in error.

であるとか

This Message was undeliverable due to the following reason:
Your message was not delivered because the return address was refused.