Stephen’s recently been questioned a bit about his email address validation regex - which has a few problems… Notably, it doesn’t allow for addresses like rob@uk, which I’m assured once existed (although I don’t believe it still does).

He wasn’t aware of any TLDs with MX records - so, of course, I had to set out to make a list. And here it is! The following TLDs (all ccTLDs, though I checked all the gTLDs I could find too) all had MX records, as of tonight

.ai - Anguilla
.as - American Samoa
.bj - Benin
.cf - Central African Republic
.cx - Christmas Island
.dj - Djibouti
.dm - Dominica
.gp - Guadeloupe
.gt - Guatemala
.hr - Croatia
.io - British Indian Ocean Territory
.kh - Cambodia
.km - Comoros
.mh - Marshall Islands
.mq - Martinique
.ne - Niger
.ni - Nicaragua
.pa - Panama
.td - Chad
.tk - Tokelau
.tl - East Timor
.ua - Ukraine
.va - Vatican City
.ws - Samoa