Gmail 550 5.1.1: email account does not exist
Gmail 550 5.1.1 is a permanent refusal: the Gmail account you sent to doesn’t exist. ReputeCast takes the address off every future send by itself, so there is nothing to fix for that address; the work is keeping new invalid addresses out of your list.
What Gmail means
Section titled “What Gmail means”The email account that you tried to reach does not exist. Please double-check the recipient’s email address for typos or unnecessary spaces.
Source: Gmail SMTP errors and codes, Google Workspace Help. Checked October 2026.
Why it happens
Section titled “Why it happens”- A typo when the contact signed up (
gmial.com, a missing letter). - The account was deleted after the contact subscribed. Old lists collect these over time.
- Fake or mistyped addresses in an imported list.
- Bots that fill in signup forms with made-up addresses.
How ReputeCast classifies it
Section titled “How ReputeCast classifies it”- Bounce class:
mailbox_unknown, from the enhanced status code 5.1.1. - Report row: Hard · unknown user, with Auto-suppressed in the Suppression column.
- Sending providers report it as a hard bounce. ReputeCast adds the address to the shared suppression list for every stream and every sending provider, and marks the contact as bounced.
- Hard and soft bounces count toward the bounce rate of a running send. Above 2.0% by default, ReputeCast auto-pauses the share of the affected mailbox provider or sending provider, or the whole campaign; see monitor a send and auto-pause.
Before you begin
Section titled “Before you begin”reports:viewto read the campaign report.subscribers:viewto look at the contacts that bounced.subscribers:verify(sensitive) to run address verification, if you use it.
Keep invalid addresses off your list
Section titled “Keep invalid addresses off your list”- See how many addresses bounced. Open Campaigns and the campaign’s Report. The Hard · unknown user row shows the count and each sending provider’s original code.
- Find where they came from. Growth sources show the bounce rate of each way contacts joined and flag a source whose bounces run at more than twice the workspace’s rate.
- Verify addresses before you mail an old list. Address verification checks a list in bulk, in the import preview, or on your signup forms as people type.
- Confirm new signups with double opt-in, so a mistyped address never becomes a subscribed contact.
- Protect your signup forms from bots; the built-in spam protection is on by default.
Check that it worked
Section titled “Check that it worked”- The next campaigns’ Hard · unknown user rows get smaller.
- The bounced addresses are in Audience, then Suppression list with their original code, and Send Readiness counts them as excluded from the next campaign’s audience.
Troubleshooting
Section titled “Troubleshooting”- An address you know works was suppressed. Gmail said the account didn’t exist when the message arrived. Check the original code in Audience, then Suppression list, column Reason · original code. If you’re sure it was a mistake, remove it with Remove from the list.
- Many 550 5.1.1 bounces right after an import. The list is old. Pause sending to it, verify it, and send to the verified part first.
- Amazon SES review warnings. A high hard-bounce rate can put an SES account under review.