552 5.3.4 Error writing message

I receive the following error message when I try to attach ANY document.
This happens even when the attachment is nowhere near 3000 KB. It happens
with either of my different internet service providers and either of my
different email account providers. I have never had this problem before. So
the problem is NOT the size of the attchment, my internet provider, my email
account provider, or me not knowing how to attach documents. Any other
ideas?

552 5.3.4 Error writing message - a message size of 3076 kilobytes exceeds
the size limit of 3074 kilobytes computed for this transaction