In reply to a post by Pheasant:

when I ping smtp.idnet.com I am getting a response from an IPV6 address

Possibly just an OS protocol precedence/preference for ipv6 over ipv4.

Using ping smtp.idnet.com -4 should force it to return an IPv4 addressed response

Indeed so and no packet loss on the IPV4 either.

Thanks.

No worries.

When Andrew returns, I think it’s traceroute time to see what’s going on there!

[SMTP server looks healthy from here and I can telnet etc. into it ]

In reply to a post by Pheasant:

No worries.

When Andrew returns, I think it’s traceroute time to see what’s going on there!

[SMTP server looks healthy from here and I can telnet etc. into it ]

If I try tracert smtp.idnet.com from my laptop I get 5 IPV6 hops to the target. If I try tracert smtp.idnet.com -4 the response is the list of usage suffixes for tracert (which includes the -4 suffix) but no routing information.

Digging a bit further there seems to be something not right about the -4 suffix on my system/connection (IDNet with Zen backhaul). Things seem to be resolving to IPV6 if available and you can't then force the IPV4 resolution. tracert google.com gives IPV6 details while tracert google.com -4 also brings up only the suffix information and no routing details. A tracert to my own website (hosted by IONOS) gives an IPV4 set of hops but adding the -4 suffix brings up the tracert options and no route again.

Probably doesn't help the OP so not one to lose any time over in this thread.

OK Andrew is back!.

Just for fun, I tried tracert smtp.idnet.com whatever that is and got three responses, one from my router, and two more. One from telehouse-gw10-10G.idnet.net and another from telehouse-gw7-10G.idnet.net. Thereafter it timed out repeatedly.

I must confess I do not know what I am talking about!!!!!!!!!!

Cheers Andrew. Can you run another traceroute from your Linux box and use the numeric IP address of the SMTP server?

Copy and paste the command and output here - remember to xxxx / obfuscate the IP address of your own router for privacy.

OK Think this is right. Linux is a little different!

1 gateway (192.***.*.*) 0516ms 0.733ms 0.999ms
2 * telehouse-gw10-10G.idnet.net (212******) 17.913ms 18.588ms
3 telehouse-gw7-10G.idnet.net (212*****) 22.489ms 23.416ms 20.580ms

Thereafter 27 groups of these ***

Hope you know what the hell I am talking about!!!!!!!

Don't know if it is relevant but I am on an exchange only line with slow ADSL2 in the middle of nowhere surrounded by cows and sheep 🙃

In reply to a post by Andrew_W:

OK Andrew is back!.

Just for fun, I tried tracert smtp.idnet.com whatever that is and got three responses, one from my router, and two more. One from telehouse-gw10-10G.idnet.net and another from telehouse-gw7-10G.idnet.net. Thereafter it timed out repeatedly.

I must confess I do not know what I am talking about!!!!!!!!!!

FYI responding to pings is optional and even when enabled is usually considered by the host to be the least important thing to do. A lot of servers and routers are configured to ignore or block pings.

Ping timeouts are thus of limited use when diagnosing network issues unless you are sure that the host is configured to respond to them.

Traceroute relies on pings to measure a route so it can return poor routing information because one or more routers is blocking or ignoring pings.

Edited by Andrue (Mon 13-Jun-22 19:10:07)

From the outside world (and indeed other IDNet connections) this SMTP server appears healthy and perfectly reachable, and appears to be fairly consistent ping response. Telnet connection to the box looks OK too and doesn’t terminate prematurely. No other ISP issues known/reported.

It’s got hallmarks of a connectivity issue - so presumably either within the OPs network or their broadband connection.

Have you any thoughts as to what to try next?

In reply to a post by Pheasant:

Have you any thoughts as to what to try next?

My sentiments entirely! 😬

Other than email, presume the connection otherwise stable and not problematic?

We could run a manual telnet connection from one of your machines to the SMTP server just to check it’s not timing out?