Plus address checker: what the +tag in an email address means and where it goes
In short: Splits an address into its mailbox and +tag, names the provider (from the domain, or the MX for a company domain), says whether that provider documents plus addressing (Gmail, Google Workspace, Microsoft 365, Proton, Fastmail) and gives the address to dedupe on, Gmail dots included. Limit: It reads the address and the domain's MX. It can't tell whether the mailbox exists or whether this domain's admin turned plus addressing off.
Plus addressing lets one mailbox receive mail at name+anything@domain: [email protected] is delivered to [email protected] when the provider supports it. Gmail, Google Workspace, Microsoft 365, Proton and Fastmail document it. Enter an address to see the base mailbox, the tag, the provider's rule and the form to use when removing duplicate sign-ups.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. See pricing
Read in your browser. For a company domain only the domain is sent, for an MX lookup; the mailbox is never contacted.
Sample result
[email protected] is delivered to the [email protected] inbox.
- Mailbox
- [email protected]
- Tag
- news
- Plus addressing
- Documented
What this means for you
Dedupe on the base address so one person gets one email.
- Mailbox and +tag split
- Provider from domain or MX
- Only documented support claimed
- Dedupe key, Gmail dots included
- Plus addressing
- Gmail
- Dedupe
By SimpleVerifier Team · Last updated
Plus addresses are real inboxes. Check the rest of the list the same way.
- Paste or export the list the address came from.
- Upload or paste it at /verify. The first 100 email checks are free with a Google sign-in, no card.
- For every list after that, Pro includes unlimited email verification. Fair use: the first 100,000 checks a month at full speed, then slower, never cut off.
How do I check where a plus address is delivered?
- Enter one address with a +, such as [email protected].
- Press Check. For a company domain, its MX records are looked up to find the provider; nothing is sent to the mailbox.
- Read the base mailbox, the tag, whether the provider documents plus addressing and the dedupe key.
- Have a list? Paste the rest of it under the result to check every address.
Example
- You enter
[email protected].- You get
- Mailbox
[email protected], tagnews, provider Gmail (plus addressing documented, dots ignored), dedupe on[email protected]. - Limits
- One address at a time; for a company domain only the domain is sent, for an MX lookup.
What is plus addressing in email?
Adding + and any text after the name: mail to jane+receipts@ lands in jane's inbox, with the tag kept in the To line so she can filter on it. It's called subaddressing in RFC 5233. Gmail supports it, Google Workspace works the same way, Microsoft 365 turns it on by default (an admin can switch it off), and Proton and Fastmail document it too.
Where a provider doesn't document it, a tagged address may be rejected as an unknown mailbox, so the checker says "not documented" rather than guessing.
Are [email protected] and [email protected] duplicates?
They reach the same inbox, so for a mailing list they are one person. On gmail.com Google also ignores dots, so [email protected] is [email protected] too. That's why sign-up forms see the same person create many free accounts; the plus addressing guide covers how to catch it without blocking legitimate tags.
On Google Workspace and every other domain, dots count: [email protected] and [email protected] can be two people. The dedupe key here only drops dots for gmail.com and googlemail.com, and only drops the tag where the provider documents plus addressing.
Should I remove plus addresses from my list?
No, not by themselves. A +tag is a choice people make to sort mail, and the inbox behind it is real. Dedupe them against the untagged address instead, so each person gets one email, and verify the list as usual; a tagged address on a provider that rejects tags fails the mailbox check like any other dead address.
Which providers document plus addressing?
| Provider | Plus addressing | Dots in the name |
|---|---|---|
| Gmail (gmail.com) | Yes | Ignored |
| Google Workspace | Yes | Count |
| Microsoft 365 | On by default; admins can turn it off | Count |
| Proton Mail, Fastmail | Yes | Count |
| Outlook.com, Yahoo, iCloud | Not documented | Count |
Who uses this tool, and for what?
- SaaS signups
- Check whether jane+trial7@ is the same person as an existing account before granting another trial account.
- Newsletter owners
- Merge subscribers who signed up with and without a tag, so they get one copy.
- Support teams
- See which mailbox a tagged address from a ticket actually belongs to.
What can’t this tool tell you?
- It reads the address and the domain's MX. It can't tell whether the mailbox exists or whether this domain's admin turned plus addressing off.
- Only + is treated as a tag. Providers that use another character, or separate alias addresses, aren't traced back.
- Provider support is taken from each provider's own documentation; where there is none, it says so.
Common questions
- What does a plus sign mean in an email address?
- Everything after the + is a tag. The provider delivers the mail to the address without it, if it supports plus addressing; Gmail, Google Workspace and Microsoft 365 do.
- Does Outlook support plus addressing?
- Microsoft 365 business mailboxes do, on by default. Microsoft doesn't document it for consumer Outlook.com and Hotmail addresses.
- Is a plus address a fake email?
- No. It reaches a real inbox. It can be a sign of someone signing up more than once, so dedupe it against the base address.
- Is anything sent to the address?
- No. For company domains only the domain's MX records are looked up; the mailbox is never contacted.
Sources
That was one address. Most people have a list.
The free checker does five addresses a minute, one at a time — fine for spot-checking, useless for a CSV of 40,000.
- Upload a CSV up to 100,000 rows
- Valid, risky and invalid exported as separate files
- Repeat checks free for 14 days, no new connections
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