How to configure Exchange Server to use port 587 for outbound mail

Question

I've just set up an Exchange Server 2019 on my own test server running Windows Server 2022. Everything works fine when port 25 is open.

But my VPS provider, where I'm planning to set up a mail server, blocks port 25 due to spam issues. Is it possible to configure Exchange Server to use port 587 for outbound mail?

As I understand for now - I need to configure Send connectors to proxy outbound mail. And I've tried to do so - just selected "Proxy through client access server" in Send connector. And it's still using port 25 ... I've tried to change port for Send connector, I’ve tried to change port for Outbound Proxy Frontend connector. Nothing helps.

Is it even possible to use port 587 to send email to other servers? Or the only way is to use smart host?

Answer 1

Hi @Konstantin ，

Is it even possible to use port 587 to send email to other servers?

No, it's not possible to do this with the native Exchange Server 2019. Port 25 is required to be open for outbound mail flow according to this official document:

Network ports for clients and mail flow in Exchange

And here's a post I found about this topic for reference. The comments there also says Exchange server requires port 25.
Change Exchange 2013 SMTP port from 25 to 587(This thread is about Exchange 2013, but the basic concepts apply to Exchange 2019 as well)
Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

Or the only way is to use smart host?

Yes. As far as I know, you would need to use smart host if you do need to use port 587 for outbound mails. For detailed instructions, you might find the information in the blog below helpful:

Solution for ISP blocks SMTP port 25
Please Note: The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

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