I use a service named Penzu for keeping a journal. It's primarily web-based, but you can make it email-based if you wish to. Basically, you'd set up a daily reminder at a specific time, and you can reply directly to that email to make a new entry.
I should point out that Penzu is not a completely free service. There is a basic free tier, and then there are paid plans with additional features.
I should point out that Penzu is not a completely free service. There is a basic free tier, and then there are paid plans with additional features.