The blacklist is a database of senders who have been reported by receivers as senders of spam. Email addresses from this list are believed to distribute spammy emails, so they are either blocked or flagged as spam in the recipient's folder.
High Volume of Mail: A server sending too many messages to subscribers in their email list can get flagged as spam.
Email Forwarding: When an IP relays spam messages to another and you forward such an email, it may appear as if you created the spam message.
Attachments: Sending too many attachments in your email marketing campaign may lead to being blacklisted.
High Bounce Rate: This rate is a strong indicator that a mailing list has not been legally obtained.
Including too Many Materials: Emails containing lots of graphics, images, and animation materials trigger spam filters.
If your company is included in a blacklist, you can submit a request for removal to the website housing the blacklist. The fundamental here is to follow their instructions carefully and obey their requests.