Wordpress Subscribe Google Groups -plugin

Adds new widget 'Subscribe Google Groups', that allows user to enter e-mail address she wants to get subscribed into admin-selected Google Group.

Behind the scenes plugin sends subscription e-mail to GROUPNAME+subscribe@googlegroups.com. If everything goes well, user gets notified for succesful operation. If WordPress detects error while subscribing, user gets error message.

Known issues

If domain for the subscribing user has published strict SPF/DMARC policies, receiving domain might reject mail sent from invalid server (server hosting the WP site).

Also, see grep -RE "(TODO|FIXME)" ..