I have had some experience with Gmail and one thing I have learned is that they don't want users using their SMTP as a sending device for bulk emails. In our office, we use Exchange which allows you to send emails from a "From" address that isn't your direct login. Most SMTP providers allow you to do this as it is a pretty standard need. If you do a Google search, you'll see this is a very common problem with Gmail so it actually is something you'll run into regardless of the platform you decide to use.
The good news is, I was able to find an article that talks about a way you CAN use Gmail to send email from multiple addresses from one SMTP login. I've tested this and it works fine. You'll just need to make sure that you update Gmail to list each email address you intend on sending email from using this address.
The one drawback is in the "From" address WILL work using the users address vs. the system SMTP setting, however, the address will also say "firstname.lastname@example.org on behalf of email@example.com".
If receiver of the email hits "reply", it will reply back to your users domain email address vs. the Gmail address which is exactly what you want.
From what I see, there is no way to get around the "behalf" in the "From" but again, this is a limitation of using Gmail as your SMTP.
One final suggestion I would make is to perhaps create a Gmail account for this purpose of sending out your SMTP email.
Danny Do Couto
Chief Operating Officer
Method Integration Inc.