Senders get blacklisted for several reasons, including:
High bounce rates: Sending emails to invalid or inactive email addresses. Spam complaints: Receiving multiple complaints from recipients marking your emails as spam. Low engagement: Poor open and click-through rates can signal that your emails are not relevant to your audience. Sending too many emails too quickly: ESPs may view this as suspicious behavior. Using spammy content: Words and phrases that trigger spam filters, like "free" or "buy now."