How to use the bulk email syntax checker
- Paste the addresses, one per line or separated by commas or semicolons. A name before the address, such as Jane <jane@example.com>, is fine.
- Optionally list words or domains to flag, such as disposable-address services. An address is flagged when its domain contains one of them.
- Open the advanced options to edit the list of domains to treat as correct. A domain one typing mistake from one of them gets a suggestion, and so does a longer name that is two mistakes away.
- Read the table, with each address marked valid, invalid, duplicate, possible typo or flagged, and a note that says why.
Formula
before the @: dotted pieces of letters, digits and !#$%&'*+/=?^_`{|}~- (up to 64 characters)
after the @: dotted parts of letters, digits and hyphens, none starting or ending with a hyphen, ending in at least two letters
duplicate: the same address when capital letters are ignored
typo: a listed domain one edit away from the address's domain (two edits when its name has 7 or more letters)
The edit distance counts single-character insertions, deletions and substitutions, and a swap of two neighboring letters, such as gmial for gmail, counts as one edit.
Ten addresses with planted problems
The list holds jane.doe@example.com and JANE.DOE@example.com, which are the same address, so the second is marked as a duplicate of number 1. sam@gmial.com is valid in shape but its domain is one edit (two letters swapped) from gmail.com, so the page suggests sam@gmail.com. alex@yahoo.con gets a suggestion of yahoo.com.
lee@@example.com has two @ signs, first..last@example.com has two dots in a row, no-at-sign.example.com has no @ and kim@example has no dot in the domain, so four are invalid. buyer@mailinator.com is flagged because its domain contains a word on the flag list. That leaves 5 of the 10 addresses valid and not repeated.
What syntax checking can and cannot do
Syntax checking finds addresses that cannot work as written: a missing @, a space, an impossible domain. It cannot tell whether a mailbox exists or whether anyone reads it, and a well-formed address can still bounce. The page uses a practical subset of the rules in RFC 5322, so it rejects some unusual but technically legal forms, such as quoted local parts and bracketed IP addresses, that real mail systems rarely use.
Duplicates are found with capital letters ignored. Mail systems treat the domain as case-insensitive and nearly all treat the local part the same way. Dots and plus tags in the part before the @ are left alone, because merging them is only safe for some providers.
Typos and flagged words
Typo suggestions use a list of common mail domains that you can edit. A suggestion is a guess: a real domain that is one edit from a common one, such as a company with a similar name, will get a suggestion it does not need, so check before changing an address. The flag list is for any word you want to notice in a domain, such as disposable-address services, and matches inside the domain only.
To pull addresses out of a longer text first, use the Email and URL Extractor. To sort and de-duplicate lines in other ways, use the Text Cleanup tool, and to match names that are close but not equal, the Fuzzy List Matcher.
Assumptions and limits
- Addresses are separated by line breaks, commas or semicolons, so an address containing a comma in quotes is not supported.
- The limits are 64 characters before the @ and 254 characters in all.
- The default domain list is an example of common mail domains and the default flag words are examples. Edit both to suit your list.
- Up to 5,000 addresses are accepted.
- Nothing typed here leaves your browser.
Frequently asked questions
Does a valid result mean the mailbox exists?
No. It only means the text has the shape of an address. To know that a mailbox exists you would need to send mail to it or ask the mail server, which this page does not do.
Why are two addresses with different capitals duplicates?
Domains are not case sensitive, and almost every mail system treats the part before the @ the same way. The page keeps the first copy and marks the later ones.
Why did it suggest a change for a real domain?
The suggestion only looks at how close the domain is to a listed one. If the domain is real and simply close to a common name, ignore the suggestion or add the domain to the list of correct domains.
Can it check the domain exists?
No. It makes no network calls. A domain can have the right shape and still not exist or accept mail.