As reported (and then included in the MIGRATION.txt)
0.4.0 checks against ANONYMOUS_REGISTER to decide
whether it registers new users or not.

This turned out to be insufficient to implement
the following situation:
- anynomous register and access for web disabled
- anonymous register for mail enabled

This is a useful configuration, because
anonymous web access reveals all details,
while mail only allows access to what
a user has reported himself or was CCed to.

I have patched mailgw.py so that it checks
against a new setting ANONYMOUS_REGISTER_MAIL
and suggest to do the same in the next release,
perhaps falling back to  ANONYMOUS_REGISTER
if NONYMOUS_REGISTER_MAIL is unset.