For somebody who doesn't do a lot of email, I have a lot of email clients on my phone. Email - EasilyDo Mail [itunes.apple.com] has been a surprise at how nice it is, especially for a v1.0 app. No Fastmail support yet, but it's coming in the next release.
Part of the reason for having so many clients, is I don't want to have to create a new app password if I wanted to switch back to an email client.