Slack for Windows

What's new in this version:

Highlights:
- Mailspring now allows you to RSVP to calendar events directly from your inbox. Messages with .ics attachments or text/calendar mime-parts are displayed in a nice expanded format. The Calendar preview is back and more features are coming soon!
- A new menu option, "Copy Mailbox Permalink", allows you to generate a mailspring:// URL for a thread. Clicking this link from another application opens the thread in Mailspring. Note: this is separate from thread sharing (public links) and only works on computers with the account synced
- The composer is faster, more reliable, and uses significantly less RAM over time thanks to a new version of the SlateJS text editor. You can also drag and drop selected text and drag/copy/paste inline images

Improvements:
- The message viewer and the composer now stretch the full width of their panels by default. To get the old behavior back, enable "Restrict width of messages to maximize readability." in Preferences > General
- Mailspring now supports snapcraft on Wayland properly
- In dark themes, copy-pasting text out of an email into the composer will no longer transfer the text color if it's the theme default
- The "Attach File" button has moved from the right to the left side of the composer's bottom bar, making it less likely that you'll tap the "Delete Draft" icon by accident
- Open tracking now correctly filters out your own tracking pixels so viewing emails doesn't trigger notifications. (This was a regression in a recent release)
- The "has: attachment" query now works when combined with other queries and search strings
- Sender name validation ("Are you sure you want to send addressed to 'Ben'?") now supports hyphenated names correctly
- On Linux, Mailspring handles icon themes without context keys properly
- The Dutch and Czech translations have been improved
- Mailspring displays a confirmation dialog before resetting accounts and settings
- Mailspring now warns if a permission error prevents it from updating it's macOS launch-on-start settings
- Incoming attachments without names are now given default names with file extensions inferred from their content type
- Mailspring no longer displays some HTML messages with specific styles at a height of 0px
- The color picker in the composer now includes a thin border so it's easier to see in all themes
- When copy-pasting out of the composer into a plain text destination, newlines and whitespace are preserved in your text and composer copy paste is generally more reliable
- Creating a signature with a <style> tag in it no longer applies the styles to the entire application window - style elements are now converted to inline styles in signatures
- On Windows, the font dropdowns in the composer no longer appear white-on-white in dark themes
- Select-all and copy paste of email message contents now works reliably in all cases

Development:
- Mailspring now uses Electron 4.2.4, which includes several security patches and minor bug fixes
- Resizing Mailspring's main window is considerably faster thanks to better use of ResizeObserver