I'm intrested in adding several intresting articles on my newsletter from other websites.
Am i allowed to do that in general or every website has it's own rules?
I don't see how this could be a problem, unless you are writing bad things about such websites and linking to them, everybody would like new traffic.
Now, if you are in fact writing not so good things, then it could be a problem and you could be held accountable for what you said.
I'd say you're safe.
Most websites have rules regarding:
But linking to their website in general, regardless if you are earning a referral fee or not, is not breaking any laws to my knowledge.