How to do Gmail Configuration With Dynamic CRM 2015?
you need to go to settings > email configuration and enter the gmail server addresses:
Bruno Lucas, Senior CRM Consultant
DynamicDay CRM Blog
Please mark my post as "Verified" If it helped to solve your problem
Are you wanting to use Gmail as the staff member's email account and integrate that with CRM (rather than using Outlook)?
If you're looking to track your emails in your GMail account from inside CRM 2013, you can do that by configuring your email router to connect to Gmail using POP3.
Suggest you start by referring to this blog from Inogic:
and this from Microsoft:
Or have I misunderstood the question?
If you just want a field to store a Gmail address for a customer...
you can use one of the three OOTB email addresses and just change the display name/label to 'Gmail'