The ability to create new bugs via email is already implemented.
http://cvs.openacs.org/browse/OpenACS/openacs-4/packages/bug-tracker/tcl/bug-tracker-callback-procs.tcl
Deds Castillo implemented it and I merged this feature back into OpenACS a while ago.
I'll see if I can dig up the actual instructions. The basic idea is to setup a catch-all incoming email to be dumped as individual files into a directory that the OpenACS instance can access.
The notifications package runs a scheduled procedure to sweep the incoming email directory. If the to address matches a certain pattern it is dispatched to a callback procedure.
There are paramters in the notifications package EmailQmailQueue (just needs to be a qmail style directory with individual email text files) and EmailQmailQueueScanP set to 1, then EmailReplyAddressPrefix which scans for incoming emails matching a pattern, defaulting to "notification-*"
In addition the bug-tracker package has a instance specific EmailPostID parameter so that the bugtracker package expects incoming email to be addressed to "notification-bug-EmailPostID" which is used to figure out which instance should receive the bug.