SMTP
452 Insufficient Storage
The requested action was not taken because the server has insufficient system storage. The server cannot accept more mail until storage is freed.
When You See This Code
When the mail server's disk is full or the recipient's mailbox has exceeded its storage quota. The server cannot store additional messages.
How to Fix
If you are the sender, retry later after the recipient frees up space. If you manage the server, clear disk space, increase quotas, or archive old messages.