Resolved Mailman keeps redirecting to HTTPS on wrong domain

[thfo]

I've got a strange issue with mailman ("Mailing Lists") on the latest Plesk Onyx on Debian 8 with installed Let's Encrypt Plugin.

If I enable "Mailing Lists" on any of my secondary domains and I try to reach http://lists.mydomain.com/cgi-bin/mailman I get redirected to its https counterpart but with the certificate of my main domain. This results in an certificate warning of course.

As there seems to be no way to automatically secure mailman with Let's Encrypt at the moment I would be happy to stop that stupid https redirect. Any ideas?

All I can tell from the redirect header is that its nginx answering.

Server: nginx
Date: Wed, 13 Sep 2017 14:49:14 GMT
Content-Type: text/html
Content-Length: 178
Connection: keep-alive
Location: https://lists.mydomain.com/cgi-bin/mailman

I did enable Let's Encrypt for this domain in the past and also disabled it just to test if the behavior changes but it didn't. I also made sure this is no caching issue of my browser.

I am struggling with this for a few days now and did not find any answer on this forum or the internets.

 

[thfo]

After a few more hours I stumbled upon a solution: Disable Permanent SEO-safe 301 redirect from HTTP to HTTPS in your main domain (the one which happens to be used as my plesk server domain). Once you do that, mailman won't be redirected to HTTPS anymore and the error is fixed.
You can then manually add an apache redirect to your main domain to have a continuous redirect to HTTPS:

RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^/?(.*) https://%{SERVER_NAME}/$1 [R,L]