Adding msfn.org in exceptions didn't work. Any ideas?

Need a little more info. are you using outlook or using web based, if using web based, which provider are you using?

Right.
Using outlook, but spam protection is enabled on the server, which I intend to keep on. Perhaps adding whole domain in exceptions list doesn't work because the headers of the notifications display the adress in some weird format like "MSFN Forums msfn-at-msfn.org"?

Can you post a screenshot of how you setup the filter?

why not...
(won't be of much use I'm afraid though)

Looks like you are using the right email address (msfn@msfn.org) but I can't understand your native language to determine how the filters are setup. Maybe someone else can?

Hm, basically the only possibilities is to add domain or a specific adress to the exceptions list.
Btw. Later I added the adress as well and it finally started to work. What I don't understand is why it's not working when "just" the domain is in the list. Could it have anything to do with the format in which the headers of notification mails are written?

Try adding:

*@msfn.org

also you can try to add the main server IP address MSFN is on and the nameservers/cname if you have hard control of the spam filter backend.

And again. It used to work with domain being added to exceptions and msfn@msfn.org as well on top of that. Not anymore.
Btw. Do you use sneakemail or not? The headers are confusing.

It is just PHP mail using IPB's interface.

No idea what you mean