Recent blockage of emails from banks

Hi Allan,

Thanks for your quick response.  As you suggested, I tried sending an email to my Cox email from the gmail account.  It did not go through, and I didn't receive an error or blocked message.

However, I went over to my business email address, sent an email to my Cox address and CC'd my gmail address, and it went through to my gmail, but not to my Cox email.  However, I did receive an error message this time:

Caution! This message was sent from outside your organization.

This is the mail system at host mx.cox.rs.oxcs.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<stevicus@cox.net>: host 127.0.0.1[127.0.0.1] said: 552 5.2.2
    <stevicus@cox.net> Quota exceeded (mailbox for user is full) (in reply to
    end of DATA command)

So, it's saying that my mailbox is full?  I've had the same account with Cox for nearly 20 years, and have had the same email address.  I've never been told that my email box is full.  Never got any notifications or anything from Cox telling me this.  I didn't even know there was a quota or a limit.