Email Syntax Checker
Test an address against the RFC rules, rule by rule.
Email List Comparison
Compare two lists: in both, only in one, only in the other.
Quick Tool Overview
The Email List Comparison tool takes two lists and returns three: what is in both, what is only in the first and what is only in the second, matching on the normalised form so tagged addresses cannot slip through.
- What it does
- Compares two email lists and splits them three ways
- You give it
- Two lists of addresses
- You get back
- In both, only in the first, and only in the second
- Matching
- Normalised by default, so plus tags cannot evade it
- Best for
- Applying a suppression list or finding new subscribers
About the Email List Comparison
Two lists, three answers: what appears in both, what is only in the first, and what is only in the second. That covers most of the list arithmetic anyone actually does.
Applying a suppression list is the common one — put your send list on the left and everyone who unsubscribed, bounced or complained on the right, and take the "only in the first" column as the list you may actually mail. Finding what is new since last month is the same operation the other way round, and the overlap column answers how much two segments duplicate each other.
Matching uses the normalised form by default, so a plus tag or a Gmail dot does not let a suppressed address slip back onto a send — which is exactly the failure that gets a sender into trouble.
Key features of the Email List Comparison
Three results at once
Overlap and both differences, each with its own count.
Suppression-safe matching
A plus tag or Gmail dot cannot sneak a suppressed address back in.
Fast on big lists
Hash lookups rather than a nested scan.
Three matching modes
Exact, case-insensitive or fully normalised.
Both lists stay private
Including the suppression list, which is a complaint record.
How to use the Email List Comparison
-
1
Paste the first list
Usually the one you intend to send to.
-
2
Paste the second
The suppression list, or last month’s export.
-
3
Choose how to match
Exact, case-insensitive or full normalisation.
-
4
Take the column you need
In both, only in the first, or only in the second.
Frequently asked questions
Put your send list first and the suppression list second, then take the "only in the first" column. That is everyone you may still mail, with every suppressed address removed.
Because an exact match lets a suppressed address back in through a plus tag or a Gmail dot. Someone who unsubscribed as ada@gmail.com should not be mailed again as ada+news@gmail.com, and normalised matching is what prevents it.
Yes. Both stay in your browser — there is no upload, which matters here more than anywhere, since a suppression list is a record of who complained.
Comparison uses a hash lookup rather than a nested scan, so lists in the hundreds of thousands compare in about a second.
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