Here is my tracert
C:\Users\me>tracert 188.8.131.52 Tracing route to au22.tmd.cloud [184.108.40.206] over a maximum of 30 hops: 1 * * * Request timed out. 2 * * * Request timed out. 3 * * * Request timed out. 4 * * * Request timed out. 5 * * * Request timed out. 6 31 ms 25 ms 25 ms 220.127.116.11 7 24 ms 25 ms 27 ms 18.104.22.168 8 23 ms 27 ms 25 ms 22.214.171.124 9 24 ms 24 ms 25 ms 126.96.36.199 10 27 ms 27 ms 27 ms 188.8.131.52 11 27 ms 27 ms 25 ms 10.74.5.5 12 44 ms 46 ms 39 ms 10.74.1.14 13 * * * Request timed out. 14 29 ms 36 ms 25 ms au22.tmd.cloud [184.108.40.206] Trace complete.
Is there any way to tell ?
That's what the tracert is for, it will show how far through the network it gets until it gets blocked. If for example you can't get past about hop 2 or 3 (in @Dave-P 's tracert) then then its probably Optus/NBN problem, but if you get past that down to hop 13/14 then is could be a problem with the web host, and anything in between its that specific transit point.
And as @Dave-P says, if you can't even ping the IP address then its is not a DNS problem. Its only a DNS problem when it can't translate au22.tmd.cloud (or those other domains) to 220.127.116.11.
So if the results indicating an optus nbn problem as noted above, what's the next step ?
Contact Optus. I recommend using messaging in the app so that you can spell out the exact problem (and provide the detail) which the operator will hopefully pass on to the networking team.
A client of mine is having a similar problem to yours it seems.
They run their own exchange server on an Optus NBN connection which is reachable from everywhere else it seems except from sites with other Optus NBN connections. Perhaps it's some internal routing issue or blocking on Optus equipment?
Its nothing fancy, just a simple HTTPS port.
I'd have thought that mail server would connect on port 25.
Can you do some tests
1) telnet to the target mailserver on port 25 from the problem network and also confirm thatworks from elsewhere
2) try a tracert both from problem network and from elsewhere
No, HTTPS for Outlook Anywhere and Webmail.
Port 25 outbound was another issue as Optus seem to block this post outbound. Thankfully with exchange you can just smarthost through Optus servers, so the blockage on port 25 is not an issue. And, like I said, HTTPS, outlook anywhere and all my other port forwards work completely fine from other networks and devices such as mobiles. Just not from (at this stage 2) Optus NBN connections.
DNS is not an issue as the problem PC's pick up the correct IP, it just doesn't route the traffic there. I haven't had a chance to do a tracert yet as I need to log into the client PC's that they are using from home, but will get to that soon.