If your mailbox is full, it is unable to accept new emails.

If this occurs, emails sent to your mailbox will be rejected and the senders mail server will be notified with a ‘Error 5.2.2 Mailbox Full’ soft bounce-back message.

A soft bounce is a temporary delivery failure.

The bounce-back message tells the sender your mailbox has reached it’s storage limit and is unable to accept the message for delivery.