Is this not achieved by Outlook, Thunderbird or other desktop email clients? I cannot stand using web based mail clients. I know OP wanted webmail, but I'm just curious if anyone else has achieved a good UX with a desktop client / Fastmail combo.
I’ve tried all email clients, either their Office365 integration sucks, or their Gmail integration sucks, or their performance sucks, or their compatibility sucks, or their UI sucks, and more frequently than not they suck in multiple of these dimensions. They also almost always lack calendar integration, which implies I need to get back to a webapp extremely often anyway.
I have surrendered, just give me a good web app and I’ll manage.
For work I use web Outlook (we're MS based). On top of that everything goes through box.com which I find quite good. Usually I have three tabs open in my browser (Firefox). Calendar, Email and Slack. Works pretty well.
I haven't used it in a couple of years but I really liked it for Gmail.
But the iOS Fastmail app is really good, so I use that on the phone.
Fastmail works well for small business (at least). The limits are high, and there are a lot of features that Gmail doesn’t have.
I don’t use the FM calendar, so I can’t speak to that.
I’ve found their file storage very helpful in moving data between disparate platforms. You can even set up small static websites.
From the research I've done, Fastmail seems to be the only non-Exchange, non-iCloud option to get push notifications in Apple's mail clients, which is a huge plus.
Meanwhile in my employment they turned off IMAP for security reasons, so I'm forced to use the Gmail web interface and it is not up to the task of the volume of email I receive at all.
It a real issue though. There aren't really any amazing email clients out there, but I guess that also means different things to different people. Development seems to have stopped after Gmail arrived, which is weird for someone like me who thinks that the Gmail interface is confusing.
If it wasn't for the fact that the majority of emails are HTML these days, I suppose Mutt or Alpine are good email clients.
Quite dislike the gmail UX, esp. regards t threads and composing new email :(