After sending an email, you receive the error message "452 4.2.2 Mailbox full." This means that the recipient's mailbox has reached its storage limit. You can adjust the storage limit of the affected email address according to the instructions.
After sending an email, you receive the following error message back via email:
452 4.2.2 Mailbox full
This is because the recipient's mailbox has reached its storage limit (quota). You can increase the storage limit of the affected email address by following the instructions Increase Mailbox Quota.