Yeh I am not so stressed too on the traffic front - as you said for mail it just doesn’t generate that much traffic.
I was testing speeds to here in SG and getting 100kB/s - no idea where the hiccup was but when I do similar setups in US/EU for other providers I still get ~100Mbits and given other installation difficulties I just gave up on IONOS. A shame coz their pricing was strong.