550 5.1.1 high
550 5.1.1 Email Account Does Not Exist (Gmail gsmtp)
Gmail rejected the message because the mailbox before the @ does not exist on an otherwise valid domain.
What you see
550-5.1.1 The email account that you tried to reach does not exist. Please try 550-5.1.1 double-checking the recipient's email address for typos or 550 5.1.1 unnecessary spaces. ... gsmtp
What’s actually happening
The message bounces back almost immediately with a 550-5.1.1 reply and a gsmtp tag at the end. The domain part resolved fine and the MX records are Google's, so DNS is not the problem. Gmail accepted the connection, ran the recipient check, and found no such user. This is a permanent (5.x.x) failure, not a temporary one, so retrying the same address changes nothing.
Common causes
- A typo in the local part, often a transposed letter or a missing character (jhon vs john).
- The account was deleted or suspended, common with ex-employees on Google Workspace domains.
- A Workspace alias or routing rule was removed, so mail to an address that used to work now lands on nothing.
- The sender's contact list holds a stale address scraped or imported years ago.
- A broken forwarding rule on the recipient's side points at a Gmail address that no longer exists.
How to fix it
- Read the full envelope address in the bounceOpen the original message in the NDR and check the exact RCPT TO. Gmail echoes the address it rejected. Look for a typo, an extra dot, or a wrong domain before assuming the account is gone.
- Send a one-off test to confirmMail the corrected address by hand from a normal client. If it lands, the bug was the typo. If it bounces 550 5.1.1 again, the mailbox really does not exist.
- Suppress the address in your sending systemA 5.1.1 is a hard bounce. Add it to your suppression list immediately. Continuing to send to known-dead Gmail addresses drives up your bounce rate and hurts your sender reputation with Google.
- Find an alternate contactIf this was a real person whose account was closed, reach them another way (phone, LinkedIn, a colleague) and capture a current address. Do not keep retrying the dead one.
- Audit forwarding if you own the recipient domainOn Workspace, check Apps > Google Workspace > Gmail > Routing and any user-level filters for forwards pointing at a deleted Gmail account, then remove or repoint them.
Stop it recurring
Run list hygiene and validate addresses at capture time so dead Gmail mailboxes get suppressed before a campaign sends to them.
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