Mailbox quota exceeded issue help

Hello
I've been trying to send an email to someone for the last few days, but I can't. Increasingly send email I get the following error message:
"[email protected] mailbox is full. You must delete some messages from e-mail box as soon as possible to avoid losing e-mail messages in the future. Please do not reply to this email. Your email won't go anywhere. Your mailbox quota has been exceeded"
I do not understand this message. I am sending this email to someone else. How can I delete this mailbox email message?
This message means and what can I do to make my emails delivered to Tom?
I am sorry the e-mail several times and I also tried to send it from my Gmail and my yahoo account but I get the same error.
Help is needed.
Thank you.
