1. Configure Gmail in you gitconfig:

[sendemail]
  smtpserver = smtp.gmail.com
  smtpserverport = 587
  smtpencryption = tls
  smtpuser = <gmail email address>
  from = <email address for From: field>

2. I recommend setting up an application-specific password in Google dedicated to git.

Account -> Security -> Connected applications and sites : Manage Access

3. Determine your revlist. To send a single commit, just use the sha. To send a range of commits, you can use start_sha..end_sha. Most likely, you'll want to send the commits made to a branch that are missing in upstream. For that, you would use: upstream/branch_name..branch_name

4. Send email:

git send-email <revlist> --to <other@user.com>

5. If you receive an error like this:

Can't locate Net/SMTP/SSL.pm in @INC (@INC contains: ...

you'll need to upgrade/install the Net::SMTP::SSL package:

sudo -H cpan Net::SMTP::SSL