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Can I use a different port (than 25) for my Office 365 Exchange Online Protection to my on premise server? My ISP is blocking port 25.

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I cannot seem to find a way to get SMTP working with my ISP who just a few days ago decided to block port 25 and claim they are not blocking any ports.  I have replaced every piece of equipment (modem, router, switches, etc.) as tests and I cannot telnet on port 25 to an outbound server, or telnet port 25 to my inbound server, but opening port 26 and also port forwarding 26 to 25 internally works fine (both cases).  To get around this, I need to setup a connector and specify either ONLY TLS connection and not port 25 at all, or some other port entirely without TLS.  At this point I'd be happy to just get my email working again - even if it means using a VPN service to encrypt the port 25 traffic (which does work, but not ideal!)

Thanks in advance!


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