You appear to be quoting a notification from the recipients mail server to the recipient, not a message from your ISP or mail client. Is that correct?
From an anti-virus web site, dated Jan 2005:
"Some forms of malicious file that are designed to disrupt the action of anti-virus scanners. These files,sometimes referred to as "zip bombs", usually take the form of innocent looking archive files that, when unpacked in order to be scanned, require enormous amounts of time, disk space, or memory."
Brightmail appears to be a corporate level anti-spam program
http://www.brightmail.com/ owned by symantec.
Mail server level AV software can be configured to disallow/strip attachments with user specified attachments. It is also configurable to open zip files and scan the content.
For example, my employer disallows zip, exe, mdb, hqx, and a large number of other formats.
Perhaps you can rename the file to (whatever.123) - in the message proper, advise the recipient to rename the file to whatever.zip. May also consider renaming the PSD to something other than template.
How large is the file? That may also be an issue, given the note above talks about large amount of time to unpack and scan...
