Add client configuration for Kaindl Network

[kaindlnetwork]

No description provided.

[babolivier]

Hey @kaindlnetwork, and thanks for your PR!

We usually prefer that providers host their own autoconfig file whenever possible. It makes maintaining the configuration file easier (by not involving a third-party like us), and clients like Thunderbird will always prefer a configuration served by the provider directly over one served by the ISP database. See this documentation for more information on how to set one up and how it's used. Would this be something you would be willing to consider?

I've also noticed you have set the domain element of the configuration file in your PR to %EMAILDOMAIN%. This will likely not do what you expect it to; this element does not accept template and so will only match emails ending with @%EMAILDOMAIN% (without replacement). If you're using the same configuration for multiple domains, you can use the base domain from the value used in MX records, see the configuration I've shared above for more information on how it's used.