Block bounces (also known as reputational bounces) are bounces where the emails could not be delivered because they were blocked by spam filters. Reasons for this could be:
- Content with suspicious words; emails that contain inappropriate words (in the text body, the subject line or the sender field) are usually rejected.
- The HTML format in the sent email differs significantly from the HTML standard.
- A recipient activated a spam filter and has put the sender on its personal spam list.
- The sender is blocklisted, which means that the contact has informed their internet provider that they consider the email received to be spam.
- Emails are rejected by the recipient’s server firewall (especially company servers).
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