Question

I want to send email with Exchange by using telnet to port 25. Until two week ago I was able to, but now a "security fix" from Microsoft has removed this possibility.

When I try, I get this message:

421 4.3.2 Service not available, closing transmission channel

What can I do?

Was it helpful?

Solution 3

I found the answer at website:

http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=2900802&SiteID=17

Thanks for your help!

Basically, this functionality was removed by default and it could be restored by means of an ad hoc configuration - but with no guarrantee that further "updates" break the system again. Thanks, Microsoft.

OTHER TIPS

I use a service (Message Labs (ML)) to filter out all the spam. We got a new internet connection and in the process of re-configuring ML's inbound/outbound services to the new IP, I got an error. So, I tested it from external by telneting to the IP on port 25 and got the "421 4.3.2 Service not available, closing transmission channel" error. What I didn't realize at first was that the reason it failed was because I had set a specific grouping of IPs on the 2007 edge server receive connector (for the ML servers). So, I added my lan network & additionally another IP for the external host I was testing from and low and behold, I could connect from both.

What I figured was happening with ML was that their server that was testing the connectivity was on an address that was excluded from the edge server.

So, I removed my testing IPs and created a new, temporary, receive connector on the edge server, accepting from all addresses (0.0.0.0 - 255.255.255.255). I then submitted the change to ML again and guess what...this time they accepted it. Now, I'll simply remove the test receive connector and everything should be golden.

SMTP is the protocol that is used to receive email from the rest of the world so I doubt that Microsoft has dropped that. There must be some other misconfiguration on your server.

Try double-checking your relay-settings and the event-log on your exchange-server.

After more than 5 years of flawless working, the 2010 EDG server suddenly stopped accepting with "421 4.3.2 Service not available". The SmtpReceive log (Get-TransportServer | select ReceiveProtocolLogPath) confirmed that it was indeed the edge server generating this error.

The EDGE server had two ip-addresses on a single NIC. After the following steps all worked fine again:

  1. remove one ip-address from the nic on the edge server
  2. update the static entry in DNS to point the second ip-address
  3. on the Default internal receive connector allow to receive mail on all available IPv4 addresses.

Notice: this setup is not a security best practice for a DMZ. Better to use two NICs each with a leg in a different zone.

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