In continuation of the KB Atricle “492-17079 - How to: Using CRM to send and receive emails with Microsoft Exchange Online (Office 365)”, if you are using Gmail instead of Exchange Online, you may face an issue when any email sent from CRM will be showing against one specific sender which is configured as SMTP USER in Email configuration. Also when the recipient receives same email and reply on that, you should expect that email back in the Mailbox of the CRM user who sent that Email.
In order to achieve this you need to do following setting in your Gmail Account:
If you are using Gmail server with Sage CRM, go to Gmail Account -> Settings -> Accounts & Imports tab, click on “Add another email address” and add all CRM user’s email account and Alias details one by one.
This will bring the reply email back to sender’s email box.