5.7.10: read the SMTP error beside the code
A 5.7.10 bounce needs its full SMTP text. Gmail uses it for commands pipelined after STARTTLS. Check the provider and diagnostic before changing TLS settings.
Keep the full diagnostic
The enhanced code alone is insufficient to name the cause. Keep the three-digit reply, the server that returned it, and the text beside it. Our diagnosis uses that context rather than assuming every 5.7.10 means a failed TLS handshake.
Gmail: commands after STARTTLS
Gmail uses 523 5.7.10 when a sending client pipelines commands after STARTTLS. Give the sending service the full error and ask it to correct its SMTP command sequencing. Changing the recipient's certificate or removing an MTA-STS policy does not address that protocol error.
Other TLS-related diagnostics
If the full text describes an encryption requirement or TLS failure, investigate that specific condition. Check sender logs and, for a receiving domain you operate, TLS-RPT reports. Those reports can provide evidence of certificate or connection failures; this code by itself cannot.
Frequently asked
What does Gmail's 523 5.7.10 mean?
Gmail documents this as an SMTP protocol violation: another command was pipelined after STARTTLS. The sending client must wait for TLS negotiation before continuing.
Does 5.7.10 prove the receiving server lacks TLS?
No. Read the provider and full diagnostic. A command-sequencing failure does not establish that encryption was unavailable or that the receiving certificate was invalid.
Should I change MTA-STS or disable TLS?
Do not weaken TLS policy based only on this code. For Gmail's sequencing error, fix the sending client's STARTTLS handling. For other diagnostics, investigate the specific TLS or SMTP failure they describe.
Forward the bounce to your workspace's private diagnose address and trustyourinbox reads it for you: the cause in plain English, the evidence from up to eight sources, what was ruled out, and a one-click DNS fix when one exists. Then a recovery watch confirms from the receivers' own reports once your mail passes again.
Keep reading
MTA-STS and TLS-RPT, explained
The policies that require TLS on the mail path and the reports that show when it fails.
Free MTA-STS validator
Check a domain's MTA-STS policy, mode, and MX matching in one run.
5.4.4 no route
The other transport-class bounce: DNS resolved but no usable mail route exists.
SMTP error codes, explained
How reply codes and enhanced status codes fit together, and which part to trust.
Why email bounces or lands in spam
The wider map of delivery failures, from transport problems to authentication.
Last verified 2026-10-23 against Google's SMTP error reference.
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