It's extremely hard to compete in a commodity market where a large corp can do a free product to drive competition away.

Gmail's promise of 1GB free storage was an incredible offer at those times, where many people used "paid" mailers. Paid as part of the Internet subscription with a worse Webmailer and less storage than Google provided.

It is especially complicated with Mail, where Anti-Spam measures make operating an own server work (on one side for filtering incoming mail, on the other side to prevent being blocked for spamming)