whoa -- I did a google search for that, and here's what I found:
This is caused by the fact, that in the course of delivery, my mail server receives from your mail server the warning message informing that it cannot receive the text (8bit). Because of this, my mail server has to encode the text in such a way, as to allow your server receive the message (7bit).
These problems are caused by the settings of Your mail server, and I strongly recommend you to contact Your provider and/or administrator. I cannot do their job for them !
Unlike the person who wrote that, I can't even appear to know the details, but it does look like perhaps your mail server stated that it was unable to accept 8-bit charsets, and so ours fell back to base-64 encoding.
One way to troubleshoot, if you can, would be to temporarily change your forwarding address to somewhere else (a gmail or yahoo account or something) and get the message to be sent again -- hopefully, the new server could handle 8-bit, and you'd see the message. If so, then you might contact your service provider to see what can be done.