Earlier quoted context omitted.
Does anything other than GMail provide SMTP? If he's just talking about setting the From: header, wouldn't that make it even more likely to be marked as spam?
No mail provider is going to be stupid enough to let a client application relay mail without the user inputing a username/password combo, and I would hope that most users these days are not dumb enough to blindly hand their mail authentication credentials to some random website. This leaves two options, forging the From: header or sending from your own domain. The former will get marked as spam by anything honoring/u…
"I would hope that most users these days are not dumb enough to blindly hand their mail authentication credentials to some random website."
That's exactly what most sites that let you import contacts ask their users to do.