Syntax question for smtp mandatory TLS encryption


I have a syntax question regarding configuring mandatory TLS encryption for the smtp process as listed on: <a href="" title=""></a>

In the second example on the page, square brackets are used when specifying the policy for specific destinations in the tls_policy file:

[]:587 encrypt protocols=TLSv1 ciphers=high

Are the square brackets only required when the port to use is specified (ie: in previous example when destination was with no port specified, I notice that the square brackets are left out) or is this syntax specifying something else ?


- J


Re: Syntax question for smtp mandatory TLS encryption

By dev rob0 at 10/11/2017 - 18:37

On Wed, Oct 11, 2017 at 05:36:07PM -0400, J Doe wrote:
The [] enclose a hostname which is to be looked up as a type A or
AAAA record. Without the [] first a lookup of type MX is done, and
where found, prioritized lookups of further hostnames (A or AAAA)
would be done.

This is not specific to TLS, it is common to transport(5) and many
similar Postfix features. The reason being, MX records exist to
control mail routing.