If you’re moving to a new computer or planning to upgrade your disk then Airmail allows you to migrate your database from your old disk to a new disk or a new mac as well, just simply copy your data from Container folders from the following path:
Simply press Shift + CMD + G you’ll notice a popup like this:
Go to following path: ~/Library/Containers/it.bloop.airmail2
Once you found the file from Containers folder please enclose back to Containers and search for it.bloop.airmail folder within Containers copy the whole it.bloop.airmail to new hard drive
Copy to following path: ~/Library/Containers/
As for the passwords for your accounts you have to manually retype them from the Airmail’s Preference. This is due to the fact that Airmail doesn’t read any of your passwords from 'Keychain Access' from your Mac and it will only store to login to the server. So, basically you can copy the entire keychain from backup from this location:~/Library/Preferences/com.apple.keychainaccess.plist
Once you have restored the com.apple.keychainaccess.plist, you no longer need to re-type your Airmail account passwords, Please note that restoring com.apple.keychainaccess.plist will also affect other apps that use 'Keychain Access' to store it’s the encryption key, certificates and passwords.