If you have a custom SSL certificate configured for SMTP TLS, git should use it.
gitMinimal
The git-send-email [0] script uses StartTLS if `smtpEncryption` is set to `tls`, which can break services that don't support StartTLS. [0]: bd42bbe1a4/git-send-email.perl (L1533) PR #1395
bd42bbe1a4/git-send-email.perl (L1533)
nixfmt