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Different types of email bounces
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One of our sending domains is temporarily blocklisted. “You should only try resending to this mail server if the bounce is due to our IP or sending domain being blocked or blocklisted. Please contact us to find out.” Mail block — relay denied
If you need to know more about a specific bounce in your report, please contact us. We can check our bounce logs for the exact error message that was returned, and investigate further. “If you're seeing bounce rates above 2% it's worth investigating the cause.” Bounce — but no email address returned