To understand why emails may not be delivered to some contacts or recipients, consider the following:

1. Verify email address syntax. Check the email address format and grammar – one small typo can cause the email to bounce or get blocked.


2. Check contact opt-in status. Make sure the contact opted-in to receive emails from your company, otherwise the email may get blocked.


3. Check the email address blacklist. See if the email address or IP address is listed on any blacklists or spam databases.


4. Check the whitelist. Make sure the sending server or IP address is whitelisted by the recipient’s server.


5. Send the same message from another email address. See if sending from a different email address yields better results.


6. Check email rejection reports. See if there are any email rejection reports that provide more details about why the email was not delivered.