Spam email and error message

[#1]

I sent an email to a client on Thursday that was tracked and she received about 100 copies of the same message. I received about the same number of error messages. A few days later, the same thing happened again and then repeated it self yesterday. Today, this same error has been running all day long.  The attached error message related to an old and unused Hubspot account. How can these repeated automessages and errors be stopped? Any assistance would be very much appreciated.

[#2]

Hi @GCMD,

That error message is usually associated with 552 errors which speak to the file size exceeding the limits established by your email server. For more information on this, I wanted to share this article.

Do the emails that are bouncing back have any attachments, large images, or large signatures associated with them? 

The more information, screenshots and details you can provide the better the Community can assist.

Thanks,

Jenny