Error: SMTP Error 420

What's Causing This Error

Only the server administrators of the receiving mail server will be able to confirm the actual issue present by this error since a GroupWise server generates it. However, this is often a result of the recipient's firewall/filter blocking the message or the server experiencing a hardware issue.

Solution - Here's How To Resolve It

You need to contact the administrator of the destination mail server to find more details about this error. In addition, you can ask the recipient to disable their firewall or run a WHOIS lookup on the mail server.