Exchange email out on port 587

eddiewickens used Ask the Experts™
I have various independent exchange servers  (various versions) at numerous sites with internet connections with numerous ISPs.
One ISP blocks all port 25 traffic. they are saying to send out on port 587.
I am trying to send out directly rather than relaying via their smtp servers

If I do this surely various emails will not be accepted by those only receiving on port 25.

Or am I missing a trick?
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I understand when an ISP blocks outbound port 25 for a residential customer, but a business class connection shouldn't do that. Name and shame! How far up their ladder have you gone to try and get that configuration changed? Are there any contract details you can angrily shake at them?

Port 587 is for users with email clients to send mail to the ISP mail server for relaying on to the destination, not for sending email directly, as you're trying to do.

You need to talk to someone at the ISP who knows their ear from a hole in the ground.
Top Expert 2011
You are not missing a trick.  If you send via port 587 - you HAVE to use a Smarthost because no-one will be receiving on port 587 apart from your Smarthost.

If you want to use DNS to send emails, you need port 25 opened up, so call your ISP and try to talk some sense into them.

Make sure you block outbound TCP port 25 for all your internal IP Addresses apart from your Exchange server and you should be safe from sending most sorts of spam that gets into your client PCs.

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