Mail SSL certificate check
Check the certificate a mail app sees when it connects to your IMAP, SMTP or POP3 server, STARTTLS ports included: whether it’s trusted, which names it covers, and when it expires.
Is this tool useful?
Why mail apps show certificate warnings
- Wrong name. The certificate is issued to a different host than the one in your settings. On shared hosting, use the name on the certificate.
- Expired. The renewal didn’t run. Most hosts renew automatically about 30 days before expiry.
- Self-signed or untrusted. The certificate isn’t signed by an authority your device trusts, or the server leaves out the intermediate certificate.
- Old TLS. TLS 1.0 and 1.1 are switched off in current versions of Apple Mail, Outlook and Thunderbird.
STARTTLS ports
Ports 143, 587, 110 and 25 begin unencrypted and switch to TLS when the client asks with STARTTLS. Most SSL checkers can’t test these because they only speak HTTPS. This one talks IMAP, SMTP or POP3 first, sends STARTTLS, and then reads the certificate the same way a mail app does.
What “trusted” means here
We verify the chain against the standard public certificate authorities (the Mozilla list that Node.js ships with). Your device uses its own list, which is nearly always the same for public certificates.
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