Connected inbox error: 'This email couldn't be sent using your connected inbox'

You might occasionally see one of your CRM emails sent from HubSpot fail with a message reading, This email couldn’t be sent using your connected inbox account [email]. Accompanying this message will be an error message reading, 550 5.7.1 Client does not have permissions to send as this sender. 

This result usually indicates that the user sending the email doesn’t have adequate permissions to send as that address from a remote client. This issue is more common with Exchange users. If you experience this problem and you do not use Exchange, please work with your IT team to resolve or contact Support.

If you are using an Exchange inbox, you should connect your Exchange account to HubSpot using the HubSpot-Exchange inbox connection to send emails from the CRM. 

If you are not using the Exchange inbox, and are instead connecting your Exchange account via IMAP, ask your IT team to assign the correct permissions to your agent user. This process typically needs to occur in Exchange and/or AD (Active Directory).

• In Exchange, ensure that your user account has the ‘NT AUTHORITY\SELF’ permission.
• In AD, navigate to the Security tab and ensure that your user has the ‘SEND AS’ permission.

When you modify user permissions in Exchange, you may need to perform this on both your internal and external connector, then restart the transport and hub services to get permissions settings to apply. If you feel this error message is incorrect, resetting specific permissions entries (such as the the NT_AUTHORITY\SELF entry for a particular user) may resolve.

For additional information, review this Active Directory documentation.

You might also need to update your allowlist to add the IP addresses that HubSpot uses to make the IMAP and SMTP connection to your mail server. Sometimes, there can be a filter on the MSA that prevents us from submitting mail some or all of the time. 

Keep in mind that depending on your configuration, the steps to resolve may vary. Contact Microsoft Support if the above steps do not resolve the issue.