I had to try three different email providers to get an email address verified.
icloud doesn't work nor does anything reliant on sendmail. The error seen was:
sendmail[669355]: 26DH5tot669355: ruleset=check_mail, arg1=<no-reply@community-mail.bt.com>, relay=outbound-dkim.eu.khoros-mail.com [34.255.61.190], reject=553 5.1.8 <no-reply@community-mail.bt.com>... Domain of sender address no-reply@community-mail.bt.com does not exist
PLEASE send emails from domains with valid MX records, if you actually want people to use these forums!
Thanks