There are thousands of blocklists out there and all of them operate a little differently and all have varying levels of reputation. There are only a dozen blocklists that really can impact delivery.
The blocklist that requires the most work from you when you request delisting is Spamhaus. Spamhaus is a trustworthy blocklist and if you are listed at Spamhaus you have made a mistake that will need to be directly addressed before the listing can be removed.
SpamCop is considered a tier one blacklist for B2B marketers but a tier 2 for B2B marketers. Marketo responds to all SpamCop listings; researching to identify the source so we can work with the customer to educate on best practices and prevent future listings.
Some blocklists require that you pay a fee to be delisted. These blocklists are not favored in the email community because they use this tactic. For the most part, Marketo advises our customers not to mind alerts of being listed on a pay-to-delist blocklist. These blocklists tend to have minimal impact to your deliverability.
For the most part blocklists are dynamic and resolve themselves in around 24 hours if the issue resolves. If the problematic sending continues, of course, the blocklist will continue to keep you listed until the problematic sending ends.
If you are blocklisted, your main concern at that point should be making sure it doesn't happen again. For steps on how to identify the problematic data source and improve your list hygiene in an effort to avoid blocklist issues, see our blocklist remediation article.