Email address length checker: 64, 254 and 63 octet limits
In short: Paste addresses and see how many octets each local part, domain, domain label and whole address uses, which ones go over a limit, and which limit it is. Counted in UTF-8 octets, with a non-ASCII domain measured in its punycode form. Limit: It measures length only; it does not check the format or whether the mailbox exists.
RFC 5321 limits the part before the @ to 64 octets and the domain to 255 octets, and the whole path, brackets included, to 256, which leaves 254 for the address. RFC 1035 limits each domain label to 63 octets. Paste a list and every address is measured against all four limits.
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Sample result
Three of five addresses are over a length limit, and the longest is 256 octets.
- Over a limit
- 3 of 5
- Local part limit
- 64 octets
- Whole address limit
- 254 octets
What this means for you
An address over a limit cannot be valid under the standard, so it is dropped before it can bounce.
- Local part, domain, label, whole address
- Counted in UTF-8 octets
- Punycode for non-ASCII domains
- CSV download
- RFC 5321
- Length
- Addresses
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
Once the lengths are within the limits, check the mailboxes.
- Download the addresses that are within the limits, or use the check button under the result.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I check whether email addresses are too long?
- Paste the addresses, one per line, or upload a CSV or TXT file. Nothing leaves your browser.
- Read the counts: how many addresses are within every limit and how many go over one.
- Look at the table, which names the limit each long address breaks and shows the octet counts.
- Download the table or the list of addresses that are within the limits, then check those at /verify.
Example
- You enter
- Five addresses at example.com-style domains: a short one, one with a 64-character local part, one with a 65-character local part, one with a 64-character domain label, and one with a 60-character local part and three 63-character labels before .com.
- You get
- Five addresses checked and three are over a limit. The 64-character local part passes and the 65-character one fails the 64-octet limit. The 64-character label fails the 63-octet label limit. The last address is 256 octets, over the 254-octet limit for a whole address, even though its domain is within 255.
- Limits
- Runs in your browser. Lengths are counted in UTF-8 octets.
What are the length limits for an email address?
RFC 5321 sets the maximum total length of a local part at 64 octets, of a domain at 255 octets, and of a reverse-path or forward-path at 256 octets including the punctuation and element separators. A path is written between angle brackets, so the address inside it has 254 octets at most. RFC 1035 limits a single label of a domain name, the text between dots, to 63 octets. The tool applies all four.
What is an octet, and why not count characters?
An octet is one byte. For plain English letters, digits and punctuation, one character is one octet, but an accented or non-Latin character takes two to four. The tool counts the UTF-8 octets of what you pasted. A domain written with non-ASCII letters is converted to its punycode form first, because that is the form it takes in DNS; the punycode converter shows it.
Why would a long address appear in a list?
Two causes are common: a form or scraper that glued extra text onto an address, and an address that is long on purpose, such as a generated tag. Over-length addresses cannot be valid under the standard, so a mail server can be expected to reject them. Addresses within the limits can still be wrong in other ways; the bulk email syntax checker checks the format and the verifier checks whether the mailbox exists.
Who uses this tool, and for what?
- Cold email senders
- Find scraped addresses with extra text stuck on the end before they bounce.
- Developers
- Pick the column size for an email field, and test a form against the limits.
- Sales ops
- Explain why a CRM or importer rejected a few rows of an otherwise clean file.
What can’t this tool tell you?
- It measures length only; it does not check the format or whether the mailbox exists.
- The 254-octet figure is the 256-octet path limit less the two brackets; some servers apply tighter limits of their own.
- An address with no @ cannot be split into parts and is reported as such.
- A non-ASCII domain the browser cannot convert is counted as typed.
Common questions
- What is the longest an email address can be?
- 254 octets in total, from the 256-octet path limit in RFC 5321 minus the two angle brackets. The part before the @ can be 64 octets and the domain 255, but the whole address is held to 254.
- Does a quoted local part count its quotes?
- Yes. The tool counts everything before the last @ exactly as written, quotes included, so a quoted address is measured by the text you have.
- Does it check that the address is valid?
- No. It checks length only. An address within the limits can still have a bad format or no mailbox behind it.
- How is a domain with accented letters counted?
- In its punycode form (xn--...), the way it travels in DNS. If the browser cannot convert it, the characters you typed are counted instead.
- How many addresses can I paste?
- As many as a 25 MB text file holds. The table shows the first rows; the download has them all.
- Is my list uploaded to SimpleVerifier?
- No. The lengths are worked out in your browser.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
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