mikel/mail — comment on commit 283890c532e29541233032b00a033695c68e1417
File: lib/mail/network/delivery_methods/sendmail.rb line 41
By bionicpill:

This sort of works with the Ubuntu sendmail emulator for nullmailer (http://manpages.ubuntu.com/manpages/hardy/man1/nbsmtp.1.html) however it ends up creating multiple copies of the to address and causes it to send duplicate emails which some email servers/clients don't do a good job of ignoring.