Reviewing an SMTP server certificate

When Send Mail cannot validate the certificate presented by an SMTP server, Certificate verification failed! shows the server hostname, the validation error, Common Name, Issuer and SHA-1/SHA-256 fingerprints. Cancel is the default button. Cancelling rejects this connection before authentication or message upload.

Choose Open certificate to inspect the public certificate in macOS's native certificate viewer or its selectable Text page. Trust editing is disabled. Copy fingerprints copies both named fingerprints. Export… saves the exact public certificate as DER (.cer) or PEM (.pem), using a native Save panel. This neither accepts the connection nor changes Keychain trust. An accepted export finishes before its owning inspector and certificate decision are released.

After checking the server with its administrator, Accept certificate permits this connection. The exception is temporary: the same Send Mail workflow can reuse it only for exactly the same hostname, port and certificate bytes. A changed certificate, another host or another port requires a new decision. The exception is not saved in Settings, Git configuration or Keychain and is not shared with other Send Mail windows.

The review applies to configured SMTP and direct SMTP, including a STARTTLS upgrade on the connection that presented the certificate. Authentication and message content wait for the decision. Encryption None retains opportunistic STARTTLS when advertised and can use plain SMTP when it is absent. Select STARTTLS or TLS in Email settings when encryption is required.

Cancel or closing the progress window aborts an active review and its owned inspector/picker. A late acceptance cannot resume a cancelled submission. A save already accepted is allowed to finish while closing waits. Quit also waits for owned transport and window cleanup. A lost final server reply may mean a message was accepted; TurtleGit reports uncertain delivery and does not automatically resend it.

This SMTP decision is separate from Git authentication and SVN certificate authentication. The existing certificate inspector screenshots show the SVN helper; they are not captures of the SMTP review window.