A FIO Address consists of a username and a domain delimited by an @ symbol, there are not specific requirements around a FIO Address username, but there are format restrictions around the FIO Address as a whole, and then separate requirements for a FIO Domain in particular
| | FIO Address (username@domain) | FIO Domain |
| Min. Chars | 3 | 1 |
| Max Chars | 64 (including FIO Domain) | 62 |
| Characters allowed | ASCII a-z 0-9 – (dash) with single @ (at sign) | ASCII a-z 0-9 – (dash |