550 5.1.1 Address does not exist

What the message looks like

• 550 5.1.1 Recipient address rejected: Address does not exist
• 550 5.1.1 User unknown
• 550-5.1.1 The email account that you tried to reach does not exist
• 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup

What it means

The receiving server looked up the address it was given and couldn't find a mailbox for it. The domain exists and accepts mail, but the part before the @ doesn't. The standard name for this status is "bad destination mailbox address". Microsoft 365 and Outlook.com use 5.1.10 for the same thing.

It's a permanent error, so the sending server won't retry. It's also the bounce most likely to get an address added to a sender's suppression list.

Common causes

• A typo in the address, such as jonh@ instead of john@.
• The mailbox has been deleted, or the person has left the company.
• An alias or forwarding address has been deleted or never existed.
• The address was made up, or scraped from somewhere it shouldn't have been.

If you're the recipient

Check the address you gave the sender is exactly right. If the address is yours and it was deleted or turned off for a while, re-enable it first, then ask the sender to send again.

If the sender already got this bounce, they may have stopped sending to you even once the address works. Ask them to remove your address from their suppression list (sometimes called a bounce list), or give them a new address.

If you're the sender

Don't keep retrying. Check the address for typos, and confirm it with the person another way if you can. If you send newsletters or account emails, remove or suppress the address so you don't keep sending to it, as repeated hard bounces hurt your sender reputation.

If you use addy.io

addy.io sends 550 5.1.1 Recipient address rejected: Address does not exist when an alias has been deleted, or when it doesn't exist and catch-all is turned off for that username or domain.

To fix it, restore the alias or create it. If a sender still isn't getting through after that, they have probably suppressed the address. See My alias is active but some sender's emails aren't arriving.

If you'd rather stop an alias receiving mail without senders getting a bounce, deactivate it instead of deleting it.