There's a closed pull request on the mblaze repository

Fix from email determination when replying to some mail group lists
https://github.com/leahneukirchen/mblaze/pull/217

Description:
I just received a mail coming from a Google Group mail list and it had
the group email as To. So my reply used the default configured mail as
from and not the correct one.

Googles mails provide the target email as Delivered-To. This patch add
this check before the To to prevent this error.