I recently tried to send an email from Outlook 2011 on my Mac that contained an attachment that was too large to send. This happened roughly two months ago and the email bounced back immediately.

Since then, I am regularly receiving error alerts stating the following

[ALERT] Message too large. http://support.google.com/mail/bin/answer.py?answer=8770

Error code 1026.

I am continually deleting these notifications and there are no email in my outbox.

How do I stop these error alerts?