<p>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.</p>

<p>When I try, I get this message:</p>

<p>421 4.3.2 Service not available, closing transmission channel</p>

<p>What can I do?</p>

[{'answer_id': 80669, 'author': 'Espo', 'author_id': 2257, 'author_profile': 'https://Stackoverflow.com/users/2257', 'pm_score': 0, 'selected': False, 'text': '<p>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.</p>\n\n<p>Try double-checking your relay-settings and the event-log on your exchange-server.</p>\n'}, {'answer_id': 81856, 'author': 'michelemarcon', 'author_id': 15173, 'author_profile': 'https://Stackoverflow.com/users/15173', 'pm_score': 1, 'selected': True, 'text': '<p>I found the answer at website:</p>\n\n<p><a href="http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=2900802&amp;SiteID=17" rel="nofollow noreferrer">http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=2900802&amp;SiteID=17</a></p>\n\n<p>Thanks for your help!</p>\n\n<p>Basically, this functionality was removed by default and it <em>could</em> be restored by means of an ad hoc configuration - but with no guarrantee that further "updates" break the system <em>again</em>. Thanks, Microsoft.</p>\n'}, {'answer_id': 3553847, 'author': 'Karl McCracken', 'author_id': 429154, 'author_profile': 'https://Stackoverflow.com/users/429154', 'pm_score': 1, 'selected': False, 'text': '<p>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 &amp; additionally another IP for the external host I was testing from and low and behold, I could connect from both.</p>\n\n<p>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.</p>\n\n<p>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.</p>\n'}, {'answer_id': 41740424, 'author': 'smartbit', 'author_id': 7440569, 'author_profile': 'https://Stackoverflow.com/users/7440569', 'pm_score': 0, 'selected': False, 'text': '<p>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 (<code>Get-TransportServer | select ReceiveProtocolLogPath</code>) confirmed that it was indeed the edge server generating this error.</p>\n\n<p>The EDGE server had two ip-addresses on a single NIC. After the following steps all worked fine again:</p>\n\n<ol>\n<li>remove one ip-address from the nic on the edge server</li>\n<li>update the static entry in DNS to point the second ip-address </li>\n<li>on the <code>Default internal receive connector</code> allow to receive mail on all available IPv4 addresses. </li>\n</ol>\n\n<p>Notice: this setup is <strong>not</strong> a security best practice for a DMZ. Better to use two NICs each with a leg in a different zone.</p>\n'}]
['https://Stackoverflow.com/questions/80655', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/15173/']