If you send any bulk email at all - by which we mean mailing list email, or many copies of identical or nearly-identical email sent to many different people - then you really need to be signed up for as many ISP Feedback Loops ("FBLs") as you can.
THE ORIGINAL EMAIL DELIVERABILITY & SENDER CERTIFICATION SERVICE - GETTING SENDERS TO THE INBOX SINCE 2003
we helped found the deliverability industry which is why spam filters and Isps respect us