I have a couple of external domains that our mail server can not connect with and the gwia log generates "420 TCP Read error"
Yet, these same external mail servers are able to successfully send emails to my users.
Besides this issue all other emails are going out OK.
When I perform a tracert I get a successful completion (it took just over a minute and my GWIA SMTP Timeout settings are at the default).

When I perform a telnet to these mail servers it connects and shows ESMTP in the response.
Can their server be setup NOT to accept SMTP, just ESMTP?

Are there any disadvantages to enabling ESMTP or should I be looking somewhere else?

As always, thanks for your responses!