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hMailserver is an open source Window e-mail server. For incoming e-mail it supports STARTTLS with the help of OpenSSL 1.1.1.
It allows configuring the cipher suites, the default is:

ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:
ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:
kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:
ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:
ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:
DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:
AES128-GCM-SHA256:AES256-GCM-SHA384:ECDHE-RSA-RC4-SHA:ECDHE-ECDSA-RC4-SHA:
AES128:AES256:RC4-SHA:HIGH:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK;

I wanted to disable AES256-GCM-SHA384 but after removing it, the cipher suite was still offered for STARTTLS (according to test site https://internet.nl)

In the end I had to remove AES128, AES256 and HIGH to stop AES256-GCM-SHA384 from appearing on STARTTLS.

How should I read this OpenSSL configuration setting? On the last line AES128 en AES256 are mentioned standalone. Doesn't this mean that any cipher with AES128 or AES256 will be allowed making the long list before that quite redundant?
The same goes for the HIGH, doesn't that make mentioning a lot of the other cipher suites redundant?

Edit: In response to questions why I want to remove ES256-GCM-SHA384: for a Dutch government contract they expect our e-mail server to score excellent at the https://internet.nl test site. On AES256-GCM-SHA384 it tells:

At least one of your mail servers supports one or more ciphers that have a phase out status, because they are known to be fragile and are at risk of becoming insufficiently secure.

That is why I am trying to disable it.

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I believe you are reading the list correctly.

While there is a large amount of redundancy in your example, I imagine that the purpose of the specific ciphers in the beginning is to establish the order of preference for specific ciphers, regardless if the same cipher ends up being part of one of the built-in lists of ciphers.

As for why you would want to remove AES256-GCM-SHA384, that is rather unclear but maybe not relevant to the question.

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  • In particular a group like AES256 adds to the end of the list all (non-1.3) suites using AES256 not already in the list. As described on the man page you linked. – dave_thompson_085 Feb 25 at 3:59

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