Email normalizer
Reduce email addresses to a canonical form so you can spot the ones that are the same mailbox wearing a different hat.
The same person, three addresses
jane.smith+shopping@gmail.com, janesmith@gmail.com and Jane.Smith@googlemail.com all deliver to one mailbox. To any ordinary de-duplication they are three different people, which means three copies of the same email, three entries in a count, and three free trials from one signup.
Reducing addresses to a canonical form makes that visible. This shows which of your addresses collapse together, and which do not.
The rules are per provider, and that is the whole difficulty
It is tempting to strip dots and plus-tags from everything. That is wrong, and wrong in the direction that causes harm.
Gmail ignores dots in the name entirely and ignores everything after a +. j.a.n.e@gmail.com and jane@gmail.com are one mailbox. googlemail.com is the same domain.
Outlook, Yahoo, Proton, Fastmail, iCloud and most others honour the plus-tag convention but treat dots as significant. jane.smith@outlook.com and janesmith@outlook.com are two different people. Strip dots there and you merge two strangers' records — which on a mailing list means sending one of them the other's mail, and in an account system means one of them can reset the other's password.
So the rules are applied by domain, and what was changed for each address is reported rather than done silently.
For a domain that is not recognised — a company's own mail server — the plus-tag is left alone, because a + is a perfectly legal part of an address and some systems do use it literally.
Case
The domain is case-insensitive by the standard, always. The local part, strictly, is not: Jane@example.com and jane@example.com are permitted to be different mailboxes.
In practice no provider anyone uses does that, so lower-casing is right — but it is worth knowing that this is a convention rather than a rule, which is why it is listed as a change that was made rather than assumed.
What this is good for
Cleaning a mailing list before an import. Finding duplicate signups. Working out whether two support tickets are the same person. Checking whether the trial abuse you suspect is actually happening.
What it is not for is blocking plus-tags at signup. People use them to organise their own mail and to find out who sold their address, and refusing them is both hostile and easily worked around.
Nothing is uploaded
A list of email addresses is personal data, and in most of the world that carries legal obligations about where it goes. It goes nowhere — this runs in the page.
Common questions
Why are dots removed for Gmail but not Outlook?
Because Gmail genuinely ignores them and Outlook does not. Stripping dots on Outlook merges two different people\u2019s addresses, which on a mailing list means sending one of them the other\u2019s mail.
Is googlemail.com the same as gmail.com?
Yes, the same mailbox. It is an older domain Google still accepts, and it is normalised here.
Should I block +tags at signup?
No. People use them to organise their mail and to find out who sold their address. Blocking them is hostile and trivially worked around.
Are email addresses really case-sensitive?
The local part is permitted to be, by the standard. No provider anyone uses treats it that way, so lower-casing is right in practice — but it is a convention, not a rule.
What happens with a company\u2019s own domain?
The +tag is left alone, because a + is a legal part of an address and some systems use it literally. Only recognised providers get provider rules applied.
Is my list uploaded?
No. A list of addresses is personal data with legal obligations attached in most of the world. It is processed in this page.