Exchange 2016 - IMAP/SMTP Auth on port 587

LuLaCeK 1

Hi guys,
need help with Outlook, to use smtp port 587 for outgoing mail.
The problem is, I cannot authenticate user on port 587 (Client Frontend Connector), but if I change SMTP port to 465 (Client Proxy connector), then AUTH is working.
The port 25, for anonymous is working, but I want to AUTH users. Why is port 465 working and 587 is rejecting AUTH?

Here are connectors permissions:

Here is the log of "Client Frontend connector":

And here is the connector cert:

Kael Yao-MSFT 37,676 Reputation points Microsoft Vendor

2021-08-03T07:56:07.2+00:00

Hi @LuLaCeK

Thanks for your detailed information.
While the settings seem correct to me.

Sorry I may need to ask a few more questions:

1) What is the detailed error when you run the "Test Account Settings" in Outlook?

2) Have you configured the following settings in Outlook?

3) Dose this issue occur on all internal and external Outlook clients or just external clients?

Thanks in advance for your update.

1 answer

LuLaCeK 1 Reputation point

2021-08-03T13:27:10.97+00:00

Hi @Kael Yao-MSFT

External client (Office 2016)

But, when I change port to 465, AUTH is working, same user name, same password. Just port is changed.

On Internal client (Office365 Client) is the same problem, but when i change port to 465 again, it is working:
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Kael Yao-MSFT 37,676 Reputation points Microsoft Vendor

2021-08-06T08:45:19+00:00

Hi,

Thanks very much for the detailed information.

While I suppose there may still be some incorrect settings on the Client Frontend <servername> receive connector.

Just to confirm it, please run this command in EMS:

Get-ReceiveConnector -Identity "MLB-EXC-01\Client Frontend MLB-EXC-01" | Format-List

And would it be possible to create a new receive connector and have it listen on port 587 as a workaround?
You may also need to add the remote ip address of the Outlook clients to the Remote network settings so the clients will use this new receive connector instead of the default one.

LuLaCeK 1 Reputation point

2021-08-09T22:44:47.48+00:00

Hi,

so I ended up by recreating all receive connectors. Recreating fixed my problem, everything is working now.

But I don't understand the Client Proxy connector.

Client Proxy – Hub transport service which accepts emails sent from frontend services and sends to mailbox transport service on port 465. This receive connector accepts proxied POP and IMAP connections sent from front end transport from receive connector called Client Frontend.

In MS's Doc is wrote "Clients don't directly connect to these connectors." In receive connector section.

I don't get, what this stand for, why are client (Outlook in my case) able to connect to this port to this connector.
Why are client able to use both 465 and 587 ports.

Kael Yao-MSFT 37,676 Reputation points Microsoft Vendor

2021-08-10T06:38:28.233+00:00

Hi,
I tested in my lab and was also able to use port 465.

Sorry I didn't find any more detailed document on this topic.

While, it is mentioned in this Exchange tech blog: Exchange TLS & SSL Best Practices
that port 465 is never supported by Exchange.

Kael Yao-MSFT 37,676 Reputation points Microsoft Vendor

2021-08-18T08:13:28.197+00:00

Hi @LuLaCeK

Just checking in to see if above information was helpful. Please let us know if you would like further assistance.

Kael Yao-MSFT 37,676 Reputation points Microsoft Vendor

2021-09-01T05:56:31.853+00:00

Hi @LuLaCeK

I am writing here to confirm with you how thing going now?
Do you need further help on this issue?
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Exchange 2016 - IMAP/SMTP Auth on port 587

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