Describe the missing service. Please provide useful links.

Gmail is one of the mail providers that is used by many people. I think adding a Gmail service to notify will attract people to use more this library.

It will be possible to implement because GMail has an API to interact. See more details: https://developers.google.com/gmail/api/quickstart/go

Describe the solution you'd like

• Add new service to send a notification via email using Gmail API

Potential libraries to use

• https://developers.google.com/gmail/api/quickstart/go