Checks an SMTP configuration end to end: the greeting, the capabilities the server announces, whether the session can be encrypted with STARTTLS or implicit TLS, whether the certificate validates, which AUTH mechanisms are offered and whether your credentials are accepted. No message is ever sent — there is no MAIL FROM, RCPT TO or DATA — and credentials are used for the single AUTH attempt, never stored. The conversation runs through this site’s endpoint, which allows public addresses only and is rate limited.
587 submission with STARTTLS · 465 implicit TLS · 25 relay · 2525 alternative
Used for one AUTH attempt and never stored. Prefer an app password.
Required. Testing other people’s mail servers with their credentials is not acceptable use.