I wanted to use gmail to send patch bomb emails directly from mercurial. I looked at..

Some additional notes that might help people.

First ensure you have Two Factor Authentication enabled for your gmail account.

Next setup an app password for mercurial

Select app - Other

Enter - mercurial

Note the app_password

Then in your hgrc file add/update the smtp section

Then when you have prepared the patch and run 

 hg email tip

Enter past the CC prompt

Hopefully the patch will be sent!

Thanks 

Nicolas