An email address can be at most 254 characters long, and the part before the @ can be no more than 64 of them. Providers are much stricter when you create an address: Gmail usernames must be 6 to 30 characters, and Apple says an iCloud Mail alias must be 3 to 20 characters.
Three layers set the email address character limit: the internet standards, your provider's username rules, and the checks on each form you use. This guide covers all three, with numbers from the RFCs and each provider's help pages. Where a company doesn't publish a number, we say so rather than guess.
Local part and domain: the two halves of an address
Every address splits at the @ sign. In jane.doe@example.com:
- The local part (
jane.doe) names the mailbox. The receiving provider decides what it means, so its rules apply here.
- The domain (
example.com) follows DNS rules. Each dot-separated piece, called a label, can be at most 63 characters (RFC 1034).
Where the 254-character maximum comes from
RFC 5321, the standard for how mail servers pass messages along (SMTP), sets the first three sizes below:
| Part | Limit | Where it's defined |
|---|
| Local part (before the @) | 64 octets | RFC 5321, section 4.5.3.1.1 |
| Domain (after the @) | 255 octets | RFC 5321, section 4.5.3.1.2 |
| Path, including punctuation | 256 octets | RFC 5321, section 4.5.3.1.3 |
| Full address, in practice | 254 octets | RFC 3696, erratum 1690 |
Add 64, one for the @, and 255, and you get 320. That's the total RFC 3696 gave when it came out in 2004. The third row is the catch. When servers exchange mail, the address travels inside a "path," which RFC 5321 defines as the address wrapped in angle brackets: <jane.doe@example.com>. A path can't exceed 256 octets, and the two brackets use two of them, leaving 254 for the address. Two errata later corrected RFC 3696's text, first to 256 and then, in erratum 1690 (verified in 2010), to 254.
So the maximum email address length is 254 characters in total, with no more than 64 before the @. RFC 5321 also says every server must accept objects of at least these sizes and that bigger ones should be avoided, so 254 is the safe ceiling at the protocol level.
The limits count octets (bytes), not letters. In a plain ASCII address, one character is one byte. In UTF-8, a non-ASCII character takes 2 to 4 bytes (RFC 3629), so accented or non-Latin letters fit fewer than 64 characters before the @.
Username rules at Gmail, iCloud, Outlook, Yahoo and Proton
This table only uses what each company states in its help pages.
| Provider | Username length | Allowed characters | Plus addressing |
|---|
| Gmail | 6–30 characters | Letters a–z, numbers 0–9, periods | Yes |
| iCloud Mail | Primary: more than 3, no maximum published. Aliases: 3–20 | Not published | Not documented |
| Outlook.com | Not published | Not published in help pages | Yes, receive-only |
| Yahoo Mail | Not published | Not published (Yahoo's own examples use numbers, underscores and dots) | Not documented |
| Proton Mail | Not published | Not published (dots, underscores and hyphens are ignored) | Yes |
Gmail
Google's rules for Gmail username length and characters: 6 to 30 characters, made of letters (a–z), numbers (0–9) and periods. Ampersands, equals signs, underscores, apostrophes, dashes, plus signs, commas and angle brackets are out, and so are two periods in a row. A username can't start or end with a period, and "abuse" and "postmaster" are reserved.
Dots don't matter in @gmail.com addresses, so john.smith@gmail.com and johnsmith@gmail.com reach the same inbox (on work or school accounts, dots do count). Google also documents plus addressing: mail sent to yourname+news@gmail.com arrives in your regular inbox, where a filter can sort it.
Google Workspace (work or school) accounts follow different guidelines: up to 64 characters for the primary address, with dashes, underscores and apostrophes allowed. If your Gmail name no longer suits you, Google says you may be able to switch to a new @gmail.com address. The old one stays on the account as an alternate, and you can't create another new Gmail address for 12 months.
iCloud Mail
Apple splits its rules for iCloud email address length across two pages. Its iCloud User Guide says you can pick any primary address as long as it's more than three characters and available. It gives no maximum for primary addresses. For aliases, Apple is exact: an alias must contain between 3 and 20 characters. Since 20 is the only maximum Apple publishes for an @icloud.com name, a name of 4 to 20 characters meets both rules as written.
Apple's help pages don't list allowed characters or a starting-character rule, so treat any list you find elsewhere as unofficial. Other rules worth knowing:
- You can't rename your primary iCloud Mail address later. Apple suggests adding an alias instead.
- You can create up to three aliases. If you have three and delete one, you must wait 7 days before creating a new one.
- Aliases can't be changed, transferred or converted to primary accounts.
- Apple doesn't document plus addressing. With an iCloud+ subscription, Hide My Email generates as many random forwarding addresses as you need.
Outlook.com
Microsoft's help pages don't publish length or character rules for new Outlook.com addresses. In a 2025 answer on Microsoft's Q&A forum, a Microsoft support specialist quoted the account system's rule: an alias or email address can contain only letters, numbers, dots, underscores and hyphens.
What Microsoft does document is "+site" addressing. Add a tag, as in name+microsoft@outlook.com, and the mail still reaches you, but you can't sign in with that version or send from it. You can also attach extra addresses to one Microsoft account as aliases. An address once used for a Microsoft account can't be reused, even if that account was closed long ago.
Yahoo Mail
Yahoo's registration help page gives no length or character rules. It suggests adding a number, underscore or dot when your ID is taken, or choosing @myyahoo.com instead of @yahoo.com. You can't change a Yahoo address afterward. Yahoo's help pages don't mention plus addressing. They document disposable addresses in the form nickname-keyword@yahoo.com instead, with up to 500 as a Yahoo Mail Plus perk and up to 3 free in regions where Mail Plus is sold.
Proton Mail
Proton doesn't publish a length limit either. It says that dots, underscores and hyphens are treated as transparent (so user.name, user_name and username are the same account) and that addresses aren't case-sensitive. Plus aliases such as name+bills@proton.me work with no setup. The main username is permanent, apart from removing those three characters or changing capitalization.
Meeting the standard doesn't mean a website will accept your address. Sites run their own checks, and those can be stricter than the RFCs.
- The browser's email field has its own definition. The HTML standard calls its rule for
type="email" inputs a "willful violation" of the email syntax standard, RFC 5322. Before the @, it accepts only ASCII letters, digits, dots and a set of symbols. Quoted names such as "jane doe"@example.com and non-ASCII names fail, even though email standards allow them.
- Some forms block plus signs. In 2025, a Microsoft support specialist confirmed that Microsoft's account system refuses plus addresses as backup emails, calling it a deliberate design choice rather than a limit of the email protocol.
- Length caps vary. Any form can set its own maximum length, lower than 254.
- Plus tags can be stripped. Mail to a plus address reaches your base address, so anyone can delete the tag and write to you directly. Use tags for sorting, not for privacy.
If a form rejects your address, drop the plus tag or use a real alias.
Keep your address short and easy to share
Every extra character is another chance for a typo when someone copies or hears your address. A few habits help:
- Use your name or a short brand name, and add numbers only if the name is taken.
- Separate words with a period. On @gmail.com it's purely visual, since dots are ignored.
- Avoid characters that are awkward to say aloud, such as underscores and hyphens.
- Use aliases or plus tags for signups instead of creating a longer address.
- Check the length before you commit. Paste the address into our character counter, choose Universal, and read the Characters and Bytes (UTF-8) figures. The byte count is what the 64 and 254 limits measure.
For sales outreach, a plain, name-based address matches the tone of a good cold email that gets replies. Subject lines have limits too: see our email subject line character limit guide, or draft a few options with the email subject line generator.
Why styled Unicode text fails in an address
Text from a bold or fancy font generator looks like ordinary letters, but each styled letter is a separate Unicode symbol. A bold 𝐛 is U+1D41B, not the keyboard b (U+0062). It's the same reason a fancy font username shows "invalid characters" on social apps.
Gmail's published rules allow only a–z, 0–9 and periods, so styled letters are out from the start. Internationalized email does exist: RFC 6531 (2012) defines the SMTPUTF8 extension, which allows UTF-8 characters in addresses, so a name can use accented or non-Latin letters. Support is still thin:
- Gmail started sending to and receiving from these addresses in 2014, but Google described creating Gmail accounts with them as a future step.
- ICANN's quarterly mail server survey across generic top-level domains found about 29% of domains with mail servers were ready for internationalized addresses in 2026, up from about 20% in 2022.
- If the receiving server doesn't support SMTPUTF8, RFC 6531 says the sender must not pass the address along and, unless the message can be rewritten, should reject it. For the sender, that means a bounce.
Domain names shut these characters out completely. The IDNA2008 rules (RFC 5892) disallow characters that Unicode compatibility normalization (NFKC) would change, and the RFC's code point table lists the mathematical bold, italic and script letters as disallowed. Emoji aren't valid domain characters under those rules either.
If you want styled text in an email, put it in the subject line or the message body instead. Our guide to bold email subject lines with Unicode covers where that renders and what it costs, including screen readers that may read styled words letter by letter.
