Emails in approval box when approved throws an error "email address is invalid"

Some emails in approval box fail to get delivered with an error message "Total 1 message(s) selected.Failed to deliver 1 message(s).
Failed to deliver below recipients. Recipients might be invalid, consider deleting the message".

This article describes some of the checks and troubleshooting steps to help in addressing the issue. 

1. Ensure that the recipient to whom the email is approved is a legitimate user 
2. Check if Email security lists that user under Manage | users , group and organization
3. If the user is valid and still the email is getting rejected, check on the firewall that's sitting infront of the mail server if any security services are preventing the attachments(if any) that are  present in the email 
4.  Make sure the webui log is set to debug logging. Try and release the message and wait for the failed message. Download the webui log and look for the recipient email address in the log towards the bottom and it should show you the response fromt he mail server. If using Hosted you can do a packet capture on the firewall on port 25 to capture the mail server response from the HES servers.
   
5. Common reason would be Insufficient system resources on the mail server which will be resolved by increasing the diskspace on the mail server and security services like GAV enabled for SMTP scanning might be blocking attachments. 
   List of IPs email will be delivered by HES are:
   For NOAM Customers: 173.240.210.0/24, 173.240.213.0/24  and 204.212.170.10
   For EU Customers: 173.240.221.0/24

If the problem still persists, please contact our technical support team.

1. Online: Visit mysonicwall.com. Once logged in select Resources & Support | Support | Create Case. 

2. By phone: please use our toll-free number at 1-888-793-2830. Please have your SonicWall serial number available to create a new support case.

If you do not have a mysonicwall.com account create one for free!