[stunnel-users] How to distinguish stunnel definition between SMTP through SSL-TLS vs. STARTTLS?

Ben Stover bxstover at yahoo.co.uk
Thu Oct 26 10:08:00 CEST 2017

As yyou know there are two types of letting a local email client connect to remote secured SMTP server:

1.) through SSL-TLS
2.) through STARTTLS

How do I distinguish betwen these connection types in the stunnel.conf setup file?

In a previous post I was told to look at the "protocol" parameter.

Ok, if I specify 


what does that mean: "Connect through SSL-TLS protocol" or "connect through STARTTLS protocol"?

It seems to me that I ALWAYS have to specify "protocol=smtp" for ALL smtp-server connects.

The stunnel documentation does not explain how to setup the *.conf file for each of the variants.

Is this done only by port number 465 vs 587?

That would mean there is a hidden configuration by convention!

What if the webhoster would set up a special mail server at port 8888?


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