"Address not found": your email wasn't delivered

The bounce is final: the code starts with 5, which means the email won't be tried again. Nothing changes until someone corrects the address.

What you'll see

Gmail

An email from "Mail Delivery Subsystem" titled "Delivery Status Notification (Failure)", with the heading "Address not found" and: Your message wasn't delivered to [address] because the address couldn't be found, or is unable to receive mail. Some say "Check for typos or unnecessary spaces and try again." instead of the last part.

550 5.1.1

The code underneath. Gmail's wording: "The email account that you tried to reach does not exist." Outlook and other services use the same code, often with "User unknown" or "RESOLVER.ADR.ExRecipNotFound; not found".

553 5.1.2

Gmail's code when the part after the @ doesn't exist: "We weren't able to find the recipient domain." Usually a typo (.con for .com) or a domain that has run out.

What to do

1. Compare the address in the bounce with the one you meant, letter by letter. Google's list of usual mistakes: a misspelling (gmal.con), a space before or after the address, dots at the end, and quotation marks inside it.
2. If you picked the address from the list your email suggests as you type, it may be an old one. Delete it from that list and type the address fresh. In Outlook on the web: start typing the name, pick the old address with the arrow keys, and press Delete.
3. Still bounces? Ask the person by phone, or check their website's contact page. People change jobs, and old addresses get deleted.
4. Run their domain (the part after the @) through Email check. If it says the domain can't be found or has no mail servers, nobody at that domain can get email right now, not just this person. Email check can't tell you whether one particular mailbox exists: only their mail server knows that.
5. Is the address in the bounce different from the one you sent to? The person may have their email forwarding to an old address. Tell them, so they can fix the forwarding.

If people who email you get this

If customers say their emails to you bounce with "Address not found", fix it the same day: you're missing every email sent to that address. The usual causes:

• The mailbox was deleted or renamed, for example when someone left and their address went with them.
• Your domain has run out, which stops your email and website together. See Keep your domain from running out.
• Your domain still sends email to an old email service. The setting that decides this is called the MX record. If you moved your email and nobody changed it, mail goes to a service that no longer has your mailboxes.

Run your own domain through Email check. Its "Receiving email" line says where email to your domain goes. If that isn't the service you pay for, send the result to whoever runs your email.

Bounces for emails you never sent

If the bounce is for an email you don't recognize, look in your Sent folder. If it isn't there, someone probably put your address on their spam: see Bounces for emails you didn't send. If it is there and you didn't write it, change your email password now.