Let hubby use your computer (just because it probably simplifies things a bit) and get himself a free account here:
https://www.gmx.co.uk/
(His tablet can use any available internet connection, such as the one from your modem or the free services available in many pubs and supermarkets. So his email account doesn't have to be with BT or with any other particular internet service provider).
Then get him to install this app onto his tablet:
https://play.google.com/store/apps/details?id=de.gmx.mobile.android.mail&hl=en_GB
He'll then be able to use his GMX account with ease.