roundup/mailgw.py has the following code:

       # XXX Don't enable. This doesn't work yet.
# 
"[^A-z.]tracker\+(?P<classname>[^\d\s]+)(?P<nodeid>\d+)\@some.dom.ain[^A-z.]"
        # handle delivery to addresses like:tracker+issue25@some.dom.ain
        # use the embedded issue number as our issue
#            issue_re = config['MAILGW_ISSUE_ADDRESS_RE']
#            if issue_re:
#                for header in ['to', 'cc', 'bcc']:
#                    addresses = message.getheader(header, '')
#                if addresses:
#                  # FIXME, this only finds the first match in the
addresses.
#                    issue = re.search(issue_re, addresses, 'i')
#                    if issue:
#                        classname = issue.group('classname')
#                        nodeid = issue.group('nodeid')
#                        break


we should make that work.