Mailguard - What is the Ham Cache?
The Ham Cache is mail that Mailguard thinks is probably legitimate mail (so-called "ham", because it's "not spam"). To view this mail and confirm (or deny) this diagnosis, visit your "ham cache" by clicking the 
[Report Spam] link. E-Mails that you find in the Ham Cache have already been queued for delivery to the intended recipient(s). Confirming an e-mail (as ham) just helps to train the system that e-mails like that e-mail are not spam.
Thank you for being a ETRN customer. Please contact us if you have any questions.
We Answer Your Questions: FAQ
Q: What is the maximum e-mail attachment size?
A: The ETRN.com e-mail servers do not limit the size of individual e-mail attachments. The ETRN.com e-mail servers do impose a 400 MB maximum total message size limit. Individual customers can choose a smaller message size limit. We can also customize the handling of "over-sized" e-mails. Please contact us to discuss your specific needs. A couple of important facts:
1. Attachments are typically encoded in what is called Base64[1]. As a result, the actual length of MIME-compliant Base64-encoded binary data is usually about 137% of the original file size.
2. E-mails often contain both plain text and HTML components. This also increases the overall size of the e-mail.