This was uncovered by theregister.co.uk reader Ed Callahan whose mother Linda Callahan was trying to sign up for a Verizon email address. She could not get it to accept her surname.
Enquiries to Verizon revealed that a partnership with Yahoo! was to blame. Yahoo! will not accept any identies which include the letters "allah".
Nor will Yahoo! accept yahoo, osama or binladen. But it will accept god, messiah, jesus, jehova, buddah, satan and both priest and pedophile.
A spokesman for Yahoo! UK said: "This sounds like a glitch. But we will get back to Ed and Lindy Callahan with a full answer as soon as possible." .