If you don't know anything about HEY, you should check out the features tour. It is a great overview that highlights many of their unique features. https://hey.com/features/the-screener
HEY also shipped with a Linux client from day one, and that's what I've been using. There is a client for each platform. https://hey.com/apps
Email signatures? https://twitter.com/dhh/status/1276311062057369600
Custom domains for individuals? https://twitter.com/jasonfried/status/1273725369489727490
IMAP is probably the only qualm I have about it so far. I understand it doesn't make sense for the HEY client, but it'd be nice to manage my email from other clients. And that's not going to happen. https://twitter.com/dhh/status/1272599759686000640
Being email such a critical service and Basecamp a relatively small company, you may wonder how reliable it is. I cannot say that the application was unresponsive or slow at any point. And it's not that they don't have traffic. https://twitter.com/dhh/status/1275511173782204416
This is an instance-of-one managed by Noel De Martin.