Currently on their 1Gbps package and it's been pretty good - apart from a couple of weeks ago when they remotely disabled the ethernet ports on the router and threw everything internally networked into chaos.
(my best guess for why they turned off the ports is they just did a big swap-out of the original NTU for a new NTU + WIFI base and -maybe- did an over-exuberant reconfiguration that caught people still on the old NTUs like us.)
Why would anyone still want to tie their email hosting to their ISP ? You change ISP, you move house and your email is at risk.
Protonmail, Tutanota or even, god forbid, Gmail. That's where you should be these days, not relying on your ISP to provide email hosting.
Or do you mean self-hosting ? i.e. allow port 25 ? Residential ISPs that allow that these days are few and far between.