It appears that the BT Mail app doesn't work when I'm traveling abroad/overseas.
It's this correct?
No, it works fine
Thanks for responding.
I've had this issue before (I'm currently in Thailand) and I see that there are several recent threads with people agreeing that it doesn't (although using VPNs seems to work for some).
I'm using the web version now on my Android phone (Edge browser) and this at least seems to work okay.
If it is working on a browser then as far as BT are concerned, it is working.
You may find that the ISP that you are using does not allow the use of the relevant ports so that you can use the BT servers when using an email client/app.