Non-existent email address. The destination mail server was unable to verify the email address used. On the other half, the receiving mail server may also present with firewall or connectivity issues.
Cause
- Receiving mail server has connectivity and firewall issue
- The recipient email address does not exist on the remote side
- The user mailbox is not local and mail relay is not yet been enable
- The recipients are outside of your domain where this is truly not allowed
- Send through a server that requires SMTP authentication
- Issue with an ISP where you can send the mail only if the From Address is from a domain that they host for you
- Recipient server is down or recipient mailbox is suspended
- Recipient mailbox is disabled
Fixes:
Step 1: Ensure Recipient Email Address Is Valid
Check with the recipient to make sure the email address given is correct.
Step 2: Contact Recipient
Contact the recipient to get more information.