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All email in Mail spool failed with "no route to host" using O365 as smarthost in MTA mode

BartJen

Hi everyone!

In my home lab running Sophos XG Home I've configured Email running as MTA using O365 as smarthost. (I'm using the MX endpoint as smarthost FQDN per this description). This setup has worked for years, somehow it broke and I'm unable to find the solution.

While the smarthost hostname nicely resolves to the required e-mail addresses, every e-mail fails in the Spool with "R=smart_host_route T=smarthost_smtp defer (113): No route to host DT=0.005s" 

For the life of me I'm unable to figure out why?! Even looking at the log via the console doesn't get met any info.

The firewall log, nor the Email log does not show any activity regarding this. 



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  • 0

    Do a packet capture on the firewall and check for Port 25. Do you see packets from 0.0.0.0 as source IP? This could be an indicate for an issue with the firewall rules. 

    Try to activate the legacy mode and switch back to the MTA mode. it will create a new firewall rule to set the outbound firewall NAT rule. 

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  • 0 in reply to LuCar Toni

    The source IP in the capture show's the WAN IP. I've removed the auto-added rule and switched legacy/MTA to have them recreated. This is the result:

    Telnet from console:

    Capture:

  • 0 in reply to BartJen

    So if even telnet does not work, there is an issue with your ISP likely. So there should be any reply by the host you try to connect. If Port2 is your correct WAN port, there should be a reply. 

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  • +1 in reply to LuCar Toni

    It is indeed my ISP :-(  .. it decided to block outgoing port 25 since 1 October 2021. Hence why it always worked and in my new lab environment not anymore.

    I was the last thing I would have suspected, Thanks for the deferent angle! 

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