Subscribe Google Groups free WordPress plugin

This plugin adds new widget ‘Subscribe Google Groups’, which allows visitors to sign up to admin-specified Google Group. After user as entered her e-mail address and submits the form, plugin (tries to) sends e-mail to GROUPNAME+subscribe@googlegroups.com. Afterwards, Google Groups sends confirmation link to submitter, and when user has clicked the link, she gets added to the group. Note: If user domain has strict SPF/DKIM policies for e-mail handling, @googlegroups.com might reject their subscription request. In this case user needs to subscribe manually (by sending mail from her e-mail client or by visiting group page.) Site can have 1-N widgets, each with their own configuration.