I always wonder about that. It seems like a non-issue to me. You’re just paying it, same as always, and the other can contribute when or if they can, what they can. Running costs that do increase with two people, like electricity or water, should be easy to just split some way, since the other’s no longer paying for their rent and utilities.
But why does it have to be some set sum or percentage or whatever? Why does it have to be static in the first place? Why not just let them contribute what they can, when they can, since the money’s not tight?
But of course the real correct answer will always be different for each relationship. And only revealed by talking and assuming each feel comfortable being honest and vocal about their thoughts and neither gets steamrolled or gets left with reservations or doubts about the outcome.
If you mean self-hosting email, then good luck.
It’s a lottery with the IP and even the IP space you get, whether anyone will actually receive your emails.
I hosted my own for a few years, but god fed up telling everyone to dig through their junk folder for my emails, and not being responded to very often, probably because of just that.
Maybe some providers have it better, but I tried a few and each was just not good. I really think Microsoft, Amazon, Google and other big players have intentionally separated the good, trusted IPs, ones they use for email services specifically, and made the other worse