When I was attempting to register for the boards, my host which has implemented Postfix SAV would not accept your web form which had an invalid 'MAIL FROM' in the SMTP Envelope:
Dec 6 14:05:28 mx3 pf-in/smtpd: NOQUEUE: reject: RCPT from coppermine.vm.bytemark.co.uk[126.96.36.199]: 554 5.1.7 <email@example.com>: Sender address rejected: undeliverable address: host a.mx.coppermine.vm.bytemark.co.uk[188.8.131.52] said: 550 Unknown user (in reply to RCPT TO command); from=<firstname.lastname@example.org> to=<MY_EMAIL_ADDRESS> proto=ESMTP helo=<coppermine.vm.bytemark.co.uk>
Your verification email has the envelope (SMTP Session, not header) MAIL FROM of
However your MX server responds 550 Invalid user when attempting to validate that address.
I had to beg my ISP to whitelist your revdns (coppermine.vm.bytemark.co.uk[184.108.40.206]), but it would be much simpler if your MAIL FROM where a valid mailbox, even if you had it delivering to |>dev/null