Outlook got updated on my iPhone last night and now they want me to agree to having my data shared with 807 partners.
Important note: I don’t use outlook as my primary email provider. I use Proton with a custom domain but I keep outlook for some old emails.
I don’t know of any company that just runs mail servers. If you’re running your own mail server, you’re likely doing it on a small virtual instance. Adding web to that is easy. If you want a web frontend for email, there are plenty of options, although personally I just use IMAP.