Add [Mailspring]/[Mail Services]

[korewatori]

Service Name

• Mailspring - It descended from Nylas Mail and is maintained by an original author. It's a fast email client written with Electron and React.
• License: GPL3
• Why do you think this helps users privacy?: It is a fast, easy to use open source email client for desktop. It doesn't currently have a mobile variant but from what I've seen it looks like it should be alright to list on here. It has a good amount of stars on the GitHub repo
• Under what section should this service be listed?: Mail Services
• Additional comments / info: <Add any additional info here> Mailspring does have a proprietary "Mailspring account" linking feature (I think it's proprietary? I'm unsure, haven't looked deep enough into it) and it can connect with Google and Outlook services to provide emails but aside from that it's 100% open source. Thanks!