Donaldson R F Email Structure Analyzer
Type one email address and see its parts, whether it follows the format rules — rule by rule — and what else can be said about it.
Format rules
More about this address
The rules of an email address
An address has a name part (also called the local part or username), an @ sign and a domain. The name part can be up to 64 characters and may use letters, digits and the symbols . _ % + - ! # $ & ' * / = ? ^ ` { | } ~, but cannot start or end with a dot or contain two dots in a row. The domain is made of labels separated by dots, each up to 63 characters, using letters, digits and hyphens (not at the start or end of a label), and the whole address can be at most 254 characters. The last label (the ending or TLD) must be at least two letters.
Some parts have special meaning to particular providers: +tag (sub-addressing) is supported by Gmail, Outlook, Apple and many others and delivers to the same mailbox; Gmail also ignores dots in the name part, so j.o.h.n@gmail.com and john@gmail.com are the same mailbox. Check a whole list at once with the email syntax validator.
Frequently asked questions
Does this check that the mailbox exists?
No. It checks the format and describes the address; only sending a message (or asking the mail server) can show whether it exists.
Why is a valid-looking address rejected?
Rare but technically allowed forms (quoted names, comments, non-English letters) are treated as invalid because most systems reject them.
Is the address sent anywhere?
No. It is analysed in your browser.