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Avoiding -420 TCP Errors

Novell Cool Solutions: Tip
By Kimberly Combest

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Posted: 5 Dec 2006


You may get an increasing number of "-420 TCP" write errors when trying to send out e-mail from your GroupWise system.


Check exceptions on relays - be sure all relays are absolutely necessary. This apparently bogs down a lot of the communication between mail servers, which may cause the 420 errors.

1. Go to Properties, Access Control, SMTP Relay Settings.

2. Remove any unnecessary IP addresses from the SMTP gateway and from the GWIA.

3. Verify that all exceptions you are allowing are really what you need.

I know there are many factors that cause these 420 errors; however, following these steps reduced our counts significantly.


We have an SMTP Gateway for incoming email, with exceptions on relaying from our ISP. We also had an outside sponsor who was allowed to relay when we originally hired them on to host.

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