We need some more information on this. I can't find the version used to report
the bug (76855b09baf7).

Probably not.
The traceback lines no longer match my version, the only reason I can see
reading the code is you try to send a patch without a commit message. It can
happen if a raw diff was imported or through convert. Maybe you remember what
the commit looked like (or maybe you can even export it and paste it here if
it's not too long) ?

I recall that I was trying to use gmail as my smtp provider. Gmail requires me
to use TLS. Perhaps this might affect it?

I have no problem under Windows with crew tip and the same script

Can you reproduce it with a standalone script ? I cannot see this error with
crew tip and the following commands:

$ hg init t
$ cd t
$ echo a > a
$ hg ci -Am t
adding a
$ cd ..
$ hg clone t t2
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd t2
$ echo a >> a
$ hg ci -Am t2
$ hg email -r 1 -t pmezard@gmail.com

C:\Workspace-HG\crew-stable-patches>hg --traceback email -r 6486 -t mercurial-de
vel@selenic.com
This patch series consists of 1 patches.

Traceback (most recent call last):
  File "mercurial\dispatch.pyc", line 45, in _runcatch
  File "mercurial\dispatch.pyc", line 364, in _dispatch
  File "mercurial\dispatch.pyc", line 417, in _runcommand
  File "mercurial\dispatch.pyc", line 373, in checkargs
  File "mercurial\dispatch.pyc", line 356, in <lambda>
  File "hgext\patchbomb.pyc", line 364, in patchbomb
  File "hgext\patchbomb.pyc", line 316, in getexportmsgs
  File "hgext\patchbomb.pyc", line 204, in makepatch
IndexError: list index out of range
** unknown exception encountered, details follow
** report bug details to http://www.selenic.com/mercurial/bts
** or mercurial@selenic.com
** Mercurial Distributed SCM (version 76855b09baf7)
Traceback (most recent call last):
  File "hg", line 20, in <module>
    mercurial.dispatch.run()
  File "mercurial\dispatch.pyc", line 20, in run
  File "mercurial\dispatch.pyc", line 29, in dispatch
  File "mercurial\dispatch.pyc", line 45, in _runcatch
  File "mercurial\dispatch.pyc", line 364, in _dispatch
  File "mercurial\dispatch.pyc", line 417, in _runcommand
  File "mercurial\dispatch.pyc", line 373, in checkargs
  File "mercurial\dispatch.pyc", line 356, in <lambda>
  File "hgext\patchbomb.pyc", line 364, in patchbomb
  File "hgext\patchbomb.pyc", line 316, in getexportmsgs
  File "hgext\patchbomb.pyc", line 204, in makepatch
IndexError: list index out of range