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Gmail address equivalence: dots are ignored, +tags are aliases — official rules, examples, and normalization algorithm
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gmail-address-aliases-dots-and-plus-tags-explained.md

Gmail Address Equivalence: Dots, Case & Plus-Tag Aliases

BLUF: For consumer @gmail.com accounts, three orthogonal rules apply: dots in the username are ignored, capitalization is ignored, and +tag suffixes deliver to the same inbox. A.B.C@gmail.com, abc@gmail.com, and AbC+Shop@gmail.com all reach the same mailbox. This does not fully apply to Google Workspace (custom domain) addresses — dots may matter there.

Quick Reference (TL;DR with Examples)

Given the address johnsmith@gmail.com, all of these deliver to the same inbox:

Address Rule(s) applied
johnsmith@gmail.com canonical
john.smith@gmail.com dots ignored
j.o.h.n.s.m.i.t.h@gmail.com dots ignored
JohnSmith@gmail.com case ignored
JOHNSMITH@GMAIL.COM case ignored
J.o.H.n.S.m.I.t.H@gmail.com dots + case
johnsmith+work@gmail.com plus alias
johnsmith+important.emails@gmail.com plus alias (dot in tag)
John.Smith+Receipts@gmail.com dots + case + plus alias
j.O.h.N.s.M.i.T.h+News.Letter@gmail.com all three combined

Use cases for + aliases:

  • You+Amazon@gmail.com — filter shopping receipts
  • you+newsletters@gmail.com — auto-label or auto-archive
  • YOU+signup2024@gmail.com — track which service leaked your address
  • Foo.Bar+Security.Alerts@gmail.com — dots + case + tag, all at once

Caveat: Some websites reject + in email fields. This is a website bug, not a Gmail limitation.

How It Works: Three Independent Rules

Rule 1: Dots Don't Matter (.)

Google canonicalizes the local part by stripping all dots before matching it to a mailbox. No one else can register a dotted variation of your username — Google treats them as the same account.

johnsmith@gmail.com  ==  john.smith@gmail.com  ==  jo.hn.sm.ith@gmail.com

"If someone accidentally adds dots to your address when emailing you, you'll still get that email. For example, if your email is johnsmith@gmail.com, you own all dotted versions of your address: john.smith@gmail.com, jo.hn.sm.ith@gmail.com, j.o.h.n.s.m.i.t.h@gmail.com" — Google Help: Dots don't matter

Exception: Google Workspace accounts on custom domains (e.g., you@yourcompany.com) do not ignore dots. john.smith@yourcompany.com and johnsmith@yourcompany.com can be different mailboxes.

Rule 2: Case Doesn't Matter

Gmail treats uppercase and lowercase letters identically. There is no dedicated Google Help article for this, but it is consistently confirmed by Google's Diamond Product Experts and is implicit in the username creation rules (which specify only a-z, not A-Z):

"Google/Gmail account names are not case sensitive, so there should be no problems receiving your mail." — Diamond Product Expert, Google Community

"Gmail has always ignored the period/dot in an email address, just as Gmail ignores capital letters." — Google Community thread

foobar@gmail.com  ==  FooBar@gmail.com  ==  FOOBAR@gmail.com  ==  fOObAr@gmail.com

Rule 3: Plus Alias (+)

Appending +tag after your username and before @gmail.com delivers mail to the base address. The +tag portion is preserved in the To: header, so you can create Gmail filters based on it.

"Messages sent to the following aliases will all go to janedoe@gmail.com: janedoe+school@gmail.com, janedoe+notes@gmail.com, janedoe+important.emails@gmail.com" — Google Help: Send from alias

Google's own examples show tags containing letters and dots (e.g., +important.emails).

What characters are officially documented in +tag?

Google describes the feature as adding "a plus sign (+) and any word" before @. Official examples use plain words and dots:

+news  +urgent  +school  +work  +shopping  +important.emails   ✅ documented
+foo-bar                                                        ⚠️ NOT in official examples
+foo+zoo-bar                                                    ⚠️ NOT in official examples

Hyphens (-) and a second + inside the tag are not shown in any Google documentation. The username creation rules explicitly say usernames can contain letters, numbers, and periods — but that rule governs the base username, not the alias suffix, so it neither confirms nor denies - or extra + in tags.

Practical advice: If you need documented-safe tags, stick to + followed by letters, numbers, and dots. Forms like +foo-bar may work empirically but are undocumented and should not be relied upon in systems where validation correctness matters.

Combining All Three

Dots, capitalization, and plus aliases are orthogonal — they compose freely:

J.aNe.DoE+Shop@gmail.com       →  delivered to janedoe@gmail.com
f.O.o.B.a.R+Travel.2026@gmail.com  →  delivered to foobar@gmail.com

Documented-Pattern Examples

All examples below use only patterns supported by official Google documentation: arbitrary dot placement, arbitrary capitalization, and one + with a tag made of letters/numbers/dots.

Given canonical address foobar@gmail.com:

Variant Mechanisms
FoObAr@gmail.com case only
Foo.Bar@gmail.com dots + case
F.o.O.b.A.r@gmail.com max dots + case
foobar+Work@gmail.com alias + case in tag
FoObAr+Work.Notes@gmail.com case + alias with dot
Foo.Bar+School.Project.Updates@gmail.com dots + case + multi-dot tag
fOObAr+Travel.Bookings.2026@gmail.com case + alias + numbers
FOObar+Receipts.Archive@gmail.com case + alias
FoO.BaR+Newsletters.Tech.AI@gmail.com dots + case + deep tag
f.o.O.b.a.R+Family.Photos.Backup@gmail.com max dots + case + deep tag
foobar+shopping.deals@gmail.com lowercase + alias with dot
foo.bar+security.alerts@gmail.com dots + alias

Safe pattern template: F.o.O.b.A.r+Tag.One.Two@gmail.com — mixed case, arbitrary dots in base, one +, tag of words and dots.

Username Constraints

  • Gmail usernames are 6–30 characters long (per Google's account creation rules).
  • Usernames can contain letters (a-z), numbers (0-9), and periods (.).
  • Usernames cannot contain &, =, _, ', -, +, ,, <, >, or consecutive dots.
  • Google does not publish a precise character grammar for the +tag portion. Officially documented examples use only letters and dots. Hyphens, underscores, and additional + signs are undocumented (see tag character details above).

"Usernames can contain letters (a-z), numbers (0-9), and periods (.). Usernames cannot contain an ampersand (&), equals sign (=), underscore (_), apostrophe ('), dash (-), plus sign (+), comma (,), brackets (<,>), or more than one period (.) in a row." — Google Help: Create a username

Normalization Algorithm

To determine if two @gmail.com addresses are equivalent:

  1. Lowercase the entire address
  2. Split at @ to get local and domain
  3. If domain is gmail.com (or googlemail.com):
    • Strip everything from the first + onward in local
    • Remove all . from local
  4. Compare the resulting local — if equal, same mailbox
Input:    J.aNe.DoE+Newsletter@Gmail.com
Step 1:   j.ane.doe+newsletter@gmail.com
Step 3a:  j.ane.doe
Step 3b:  janedoe
Result:   janedoe@gmail.com

Note: googlemail.com is an equivalent domain to gmail.com in countries where the gmail trademark was initially contested (e.g., UK, Germany). The same dot/case/plus rules apply.

Practical Implications

  • De-duplication: If you store user emails, normalize (lowercase + strip dots + strip +tag) before comparing to avoid duplicate accounts.
  • Filtering: Create + aliases per service, then build Gmail filters on the To: address.
  • Spam tracking: If You+SomeService@gmail.com starts receiving spam, you know who leaked it.
  • Security: Do not rely on + aliases, dot variations, or capitalization as distinct identities — they are trivially normalizable.

References

  1. Google Help — "Dots don't matter in Gmail addresses" https://support.google.com/mail/answer/7436150 — Official documentation of the dot-ignoring rule and the Workspace exception.

  2. Google Help — "Send emails from a different address or alias" https://support.google.com/mail/answer/22370 — Documents + alias behavior with examples (+work, +news, +shopping, +important.emails).

  3. Google Workspace Help — "Use Gmail aliases" https://support.google.com/a/users/answer/9282734 — Workspace-oriented alias documentation; describes + as "a plus sign and any word."

  4. Google Help — "Create a username" https://support.google.com/mail/answer/9211434 — Username length (6–30 chars), allowed characters, and explicit list of forbidden characters.

  5. Google Community — Case insensitivity confirmation (Diamond Product Expert) https://support.google.com/accounts/thread/170613265 — "Google/Gmail account names are not case sensitive."

  6. Google Community — Dots and case confirmation https://support.google.com/mail/thread/177839873 — "Gmail has always ignored the period/dot in an email address, just as Gmail ignores capital letters."

  7. Google Community — Case insensitivity confirmation https://support.google.com/mail/thread/279696101 — "Gmail addresses are NOT case sensitive."

  8. SupEd — "How does Gmail handle dots in email addresses?" https://www.suped.com/knowledge/email-deliverability/technical/how-does-gmail-handle-dots-in-email-addresses-and-can-it-cause-issues — Third-party summary consolidating Google's official alias examples.

  9. RFC 5321 §2.4 — SMTP local-part is technically case-sensitive per the standard, but Gmail (and most providers) treat it as case-insensitive in practice.

Last verified: 2025-03 against Google Help pages. Updated 2026-03 with case-insensitivity rules, tag character clarifications, and mixed-case examples.

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