Error/delay in accessing SMTP server send.one.com

[NigNic]

• When I send email from Outlook on my PC for the domain hayatministries.org there is a long delay before the email is actually sent. I have a wired connection to my computer so there is no WiFi involvement.
  
  
• If I try and send email from Outlook on my Android phone for the same domain while connected to WiFi the send fails.
  
  
• If I turn off WiFi on my phone I can send mail without any problem using my mobile data connection.
  
  
• The SMTP server is send.one.com.
  
  
• I have no problem sending email for another domain which uses SMTP server imap.ionos.co.uk from my PC or phone.
  
  
• "tracert imap.ionos.co.uk" succeeds.
• "tracert send.one.com" times out.

tracert imap.ionos.co.uk

Tracing route to imap.ionos.co.uk [212.227.15.154]
over a maximum of 30 hops:

1 <1 ms <1 ms <1 ms SkyRouter.Home [192.168.0.1]
2 2 ms 3 ms 2 ms 2.127.238.242
3 3 ms 4 ms 4 ms 89.200.132.135
4 3 ms 3 ms 4 ms 2.120.13.95
5 18 ms 18 ms 17 ms ae-19.bb-b.fr7.fra.de.net.ionos.com [212.227.120.32]
6 16 ms 16 ms 16 ms lo0-0.bb-a.wm.fra.de.net.ionos.com [212.227.117.1]
7 20 ms 20 ms 20 ms lo-0-0.rc-a.bap.rhr.de.net.ionos.com [212.227.117.208]
8 20 ms 19 ms 19 ms lo-0-0.gw-diste2-a.bap.rhr.de.net.ionos.com [212.227.112.220]
9 19 ms 19 ms 19 ms imap.1and1.co.uk [212.227.15.154]

tracert send.one.com

Tracing route to send.one.com [2a02:2350:5:20e::1]
over a maximum of 30 hops:

1 1 ms <1 ms 1 ms 2a02:c7c:f4fc:c800::1
2 * * * Request timed out.
3 5 ms 4 ms 4 ms be1028.er16.thlon.isp.sky.com [2001:7f8:4::15e7:1]
4 * * * Request timed out.

It's interesting that the first node in the route is different for the two SMTP servers.

[do-nowt]

Hi @NigNic ,

The server "send.one.com" has both IPv4 and IPv6 addresses (which is not particularly unusual) :

$ host send.one.com
send.one.com has address 46.30.211.140
send.one.com has address 46.30.211.141
send.one.com has IPv6 address 2a02:2350:5:20e::1
send.one.com has IPv6 address 2a02:2350:5:20e::2

But the IPv6 addresses don't appear to be responding to SMTP attempts:

$ nc -6 send.one.com. 587

(just times out)

But it works find on IPv4:

$ nc -4 send.one.com. 587
220 mailrelay6.pub.mailoutpod2-cph3.one.com ESMTP
quit
221 2.0.0 Bye

I tried this from both a NowTV/Sky connection, and then a VPS on a completly different ISP and saw the same, so I don't think it is a sky issue. Probably best if you contact the support for "one.com" and ask them to check their end.

The delay will be your system trying to send using IPv6, then giving up after a couple of minutes and falling back to IPv4 which then works. When you turn WiFi off and use the phone GSM network, you will often only be using IPv4 so thats why that works. Similarly, from any ISP that didnt support IPv6 you wouldn't notice an issue.

[NigNic]

Thank you @do-nowt for your investigation and reply. 

When you say, "The delay will be your system trying to send using IPv6", what is deciding to use IPv6? Is it my PC/phone or the Outlook app or the ISP? I'm wondering if somewhere I can force the use of IPv4.

[do-nowt]

It will be the OS (Windows/Android etc) deciding, typically they will prefer IPv6 when available and try that first. You can turn it off in Windows in the properties of the ethernet or wifi connection. I don't know if you can turn it off in Android. It might be possible to turn it off in the router but I'm not familiar with Sky routers. (The best way would be to get "one.com" to fix it on their server.)