fixed variable name
(cherry picked from commit 19c80a83a2819bdac73dfe4bc08e270205a9a666)
Add support for mail sending via msmtp

(adapted cherry-pick from commit 7f8b9b6e2fb49ce3bae166674a06754e5940ea04 of Dosenpfand)
Some little modifications and additions in the doc of the config file