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We are testing Exchange Server 2016 mail server. We can connect to user's mailbox via OWA (Outlook Web Access). When testing POP3 mail from Microsoft Outlook (on a non domain-joined PC) we can send test email but can not login to POP3 server. The error message says:

(Log onto incoming mail server (POP3): The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP))

  • Incoming server port: 110
  • Outgoing server port: 25 (no encrypted)

Even when I turn off all firewalls, it still cannot connect. I have the same problem with IMAP. Do you have any ideas, please?

SamErde
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SpiderlinK
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2 Answers2

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Why are you using POP3 with Exchange? Therefore my first suggestion would be to drop that idea. If you are going to use POP3, then any old email server would do. Use Outlook Anywhere, no issues with connectivity and it is how it is designed.

The configuration you are trying to use will not work out of the box. As well as the POP3/IMAP services not being started, you cannot send email on port 25. Exchange is configured by default to only accept email on port 25, it will not relay which is what is required for use with POP3/IMAP clients. Furthermore, a lot of ISPs (although not enough of them) will block port 25 outbound, so you have to use a different port.

You need to use the Client Receive Connector, which runs on a different port to 25, it also uses SSL and if you authenticate then you can relay. In the POP3/IMAP client you need to specifically set outbound server credentials - the setting to use the same as inbound does not work.

Sembee
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  • Thanks for your reply. Yes I know it is unusual, but the problem is we could access users' mailbox via OWA but MS Outlook keep notifying errors. We also can get access via Mobile devices (Android, IOS). That's why I tried with POP, IMAP but still no luck. Do you know any document or full article that I should follow? I found some on the Internet but they were not official and not enough to cover everything in Exchange 2016. – SpiderlinK Apr 17 '17 at 15:36
  • Now I can access Exchange mailboxes via Outlook by manually settings Outlook anywhere. However, it keep asking credential when I open the Outlook even when I choose the option "Remember password". Do you have any suggestion? – SpiderlinK Apr 18 '17 at 09:06
  • Do you have a trusted SSL certificate in place? If not then that will be the issue. You need to use a trusted SSL certificate with Outlook Anywhere. You also need to decide how you are going to do Autodiscover. With Exchange 2016 Autodiscover is not optional. The easiest method is to get a UC type certificate and configure Autodiscover.example.com as one of the additional names on the certificate. You would need to add that to your DNS. Autodiscover isn't new - it hasn't changed since the release of 2007! – Sembee Apr 18 '17 at 13:54
  • Yes, I added Comodo certificate (for 90 days) and it has multiple domains (including autodiscover.mydomain.com as you suggested), but the problem still exists when opening MS Outlook. – SpiderlinK Apr 19 '17 at 01:07
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In a default installation of the Exchange Server, the POP3 and IMAP services are not running after starting the server. Please go to Computer Management (Run "compmgmt.msc") and check if the services for Exchange POP3 and IMAP are running. After you checked that, go to the Exchange Management site and activate the features POP3 and/or IMAP for the specific users.

TooCloudy
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  • Yes, I started those services before and saw them enabled on users' ECP page. Still cannot connect to POP3 via Outlook ;( – SpiderlinK Apr 17 '17 at 10:10
  • Have you done all steps from the Technet article to activate POP3 and IMAP? You can find a pretty good step by step description at the following link: https://technet.microsoft.com/en-US/library/bb124934(v=exchg.160).aspx – TooCloudy Apr 17 '17 at 10:13
  • I followed and test the result with POP test: The POP service is being tested.   There was an error testing the POP service: Additional Details S: C: CAPA S: Microsoft.Exchange.Tools.ExRca.Tests.ImapPop.MailProtocolException at Microsoft.Exchange.Tools.ExRca.Tests.ImapPop.Pop3ProtocolTester.SendCommand(String command, String logString) at Microsoft.Exchange.Tools.ExRca.Tests.ImapPop.MailProtocolTester.SecureConnection() at Microsoft.Exchange.Tools.ExRca.Tests.ImapPop.BaseProtocolTest.PerformTestReally() Elapsed Time: 429 ms. – SpiderlinK Apr 17 '17 at 15:23
  • This was the IMAP result: Additional Details   System.IO.IOException: Authentication failed because the remote party has closed the transport stream.at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest) – SpiderlinK Apr 17 '17 at 15:29
  • I also got SSL error and autodiscover erros, what should I do? Do you know any document or full article that I should follow? I found some on the Internet but they were not official and not enough to cover everything in Exchange 2016. – SpiderlinK Apr 17 '17 at 15:33
  • Now I can access Exchange mailboxes via Outlook by manually settings Outlook anywhere. However, it keep asking credential when I open the Outlook even when I choose the option "Remember password". Do you have any suggestion? – SpiderlinK Apr 18 '17 at 09:07