On another forum I'm "talking" to a person who uses a Gmail account, and on some online job applications, it rejects his email and says, "Please enter a valid email address." At first I thought he might have an email address with some of the characters that are technically allowed in the RFC, but that not all systems support. But when I found out he uses a Gmail address, I wondered: do any online job application systems restrict Gmail addresses as a spam prevention tactic?