I followed these instructions and the previous Squarespace instructions but could not get the verification email to my forwarded address. Instead, I get a bounceback response from <mailer-daemon@googlemail.com> that states...
Message not delivered
Your message couldn't be delivered to <name@yourdomain.com> because the remote server is misconfigured. See technical details below for more information.
The response from the remote server was:
550 5.7.1 Relaying denied