Aqua Mail is not cloud based. It connects to your mail servers directly from the phone and nowhere else.
You're getting a DNS error - Unable to resolve host "mywebsite.co.uk"
This error comes from low levels of Android's networking stack. We don't mess with that at all.
And so I still think the issue is on your end (the hosting provider, maybe the internet provider that your phone is connected to) and not in the app.
Maybe the internet provider's DNS server cached a "not valid hostname" report from upstream (your hosting provider) for too long. Maybe Android did.
I'd try rebooting the phone and / or using a different type of network connection as a test (mobile vs. WiFi).
But a DNS error would not be an issue "in" Aqua Mail - it's something external to the app
Oh and we don't do any "caching" (
) of DNS lookups (but your internet provider or Android itself very well might).