Your email itself lives on your mail server, so the simplest move is to install Mailspring on the new computer and add your accounts again. If you'd like to keep your settings, signatures, templates, shortcuts, and mail rules, copy Mailspring's data folder as well.

Copying your settings

1. Quit Mailspring completely on both computers (check the tray / menu bar icon).
2. On the old computer, copy the whole data folder:
   • macOS: ~/Library/Application Support/Mailspring
   • Windows: %AppData%\Mailspring
   • Linux: ~/.config/Mailspring (or $XDG_CONFIG_HOME/Mailspring; for the snap it's ~/snap/mailspring/common)
3. On the new computer, install Mailspring, launch it once, quit it, and replace its data folder with the copy.
4. Start Mailspring. Sign in to your Mailspring ID when asked, then open Preferences > Accounts and click Reconnect on each account.

You can leave out the big files: edgehill.db (the mail cache) and the files folder (cached attachments) are rebuilt from the server. Everything else is small: config.json holds accounts, preferences, and signatures; keymap.json your custom shortcuts; templates your Quick Reply templates. Mail rules are stored in the app's local storage folder, so copy the whole folder rather than just config.json if you want to keep them.

What follows your Mailspring ID

Snooze dates, Send Later schedules, reminders, read receipts, and shared-thread links are stored with your Mailspring ID, so they appear on any computer where you sign in with it. The work itself — sending a scheduled message, returning a snoozed thread — is done by whichever computer is running Mailspring at the time. Keep the old install signed out or removed so two copies don't both try to do it.

Running two computers at once

Mailspring is happy to run on several machines with the same accounts and Mailspring ID (your subscription covers all of them). Settings don't sync between machines yet; repeat the copy above whenever you want to bring one in line with the other.