Wheyll...
- Yes, there is a way to configure an outgoing server override for when the device is connected WiFi. Some residential ISPs need that.
This is configured on each account's Outgoing server settings screen (a checkbox near the bottom), under Account setup (during initial setup - press Manual then Next, for an existing account long press it in the account list and choose Account setup).
- On the other hand, if your device's current connectivity is mobile data, *and*, as you mentioned, the mobile provider deliberately blocks mail server connections, well..... AquaMail won't be able to create a miracle.
A very shady "business" practice, BTW.