There are several reasons why an IP address might get blocked:
High Spam Complaints: If recipients frequently mark your emails as spam, your IP address can be flagged. Sending to Inactive or Incorrect Email Addresses: Continuously sending emails to addresses that bounce back can lead to an IP block. Sudden Increase in Email Volume: A sudden spike in the number of emails sent from your IP can raise red flags. Blacklisting: Being listed on blacklists such as Spamhaus or Barracuda can result in an IP block.