[Cryptography] How to get certificates on email server?
John Denker
jsd at av8n.com
Mon Apr 18 14:48:15 EDT 2016
On 04/18/2016 10:52 AM, hbaker1 wrote:
> Stupid question: I'm getting a certificate error when attempting to
> send email. My email program says that the certification chain can't
> be verified.
>
> Before I accept this dubious certificate, I'd like to look up this
> server's certificate myself & check it by hand.
>
> How to do this? (Either Windows or Linux is fine, since I'm not
> trying to actually send mail; just check the certificate.)
:| openssl s_client -connect av8n.com:465
Or for even more detail:
:| openssl s_client -debug -tlsextdebug -showcerts -connect av8n.com:465
On some old buggy versions the following works better:
:| openssl s_client -CApath /etc/ssl/certs -connect av8n.com:465
Port numbers of interest include
urd 465/tcp ssmtp smtps # URL Rendesvous Directory for SSM
submission 587/tcp # Submission [RFC4409]
https 443/tcp # http protocol over TLS/SSL
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