I want to create a generic rule that moves all legitimate newsletters, mailing list emails, etc. to one single email folder so they do not clutter up my inbox.
This is not about spam or filtering it, I am just talking about emails I signed up for and want to receive. For the purpose of this question, let's just assume that spam gets filtered earlier in the process on the mailserver by the provider. If an occasional spam email gets through and also matches the rule patterns, then that's acceptable.
Of course I could create a separate rule for each newsletter email From address, but I do not want to manage all those addresses explicitly, since they can also change without notice or warning on the senders side.
So what I am looking for is basically a comprehensive list of header strings that legitimate newsletter emails would have, such as:
Precedence: bulk
List-Unsubscribe:
X-Mailer: Mailchimp Mailer
...
Again, it does not have to be perfect, I know that it's tricky because of spam. I just want a list of likely patterns to identify newsletters once the emails make it through to my inbox (after serverside spam-filtering which is very reliable).
What are additional patterns I could check?
After some research and trial-and-error, apparently the best way is to use
List-Unsubscribe:
This is described in https://www.ietf.org/rfc/rfc2369.txt and endorsed by Google and Microsoft.