Cannot send emails from Penang

[scldad]

I have been using roundcubemail for nine years and have happily accessed my mail server from all over the world.
However, I am now in Penang and can download incoming emails without issue but any attempt to send email gives an authorisation error.
I have tried connecting via my hotel WiFi and via mobile phone. No difference.
Nothing has changed at my server and nothing apart from location has changed on my Android devices  (three thereof).

PHP Error. Invalid response code from server.
Version 1.6.15. Rocky Linux server. Android clients.

HELP!!

[SKaero]

What response code is the browser receiving and can you very what the server is sending?

[SKaero]

There really isn't much information to go off of there without knowing what the device is getting or the server is sending there isn't anything to go off of.

[SKaero]

That would point to the mail server doing something odd, maybe enable smtp_debug and post that log?

[SKaero]

It should since Roundcube is sending the email from the server its hosted on so the IP shouldn't be changing.