Where does OS-X store Mail.app data - and likewise for other email clients

Solution 1:

Mail.app

Mail.app stores messages as .emlx files in ~/Library/Mail/TYPE-ACCOUNT/ eg. ~/Library/Mail/[email protected]/

Thunderbird

Thunderbird stores it's data in ~/Library/Thunderbird/Profiles/[string].default/. There are two folders, one called Mail that will hold the Local Folders and if you have an IMAP account a folder called ImapMail that will hold the IMAP messages if downloaded. The [string] is a random alphanumeric string.

Postbox

Postbox which is based off of Thunderbird stores it in much the same manner but at ~/Library/Application Support/Postbox/[string].default/.

GyazMail

GyazMail stores it's data in ~/Library/Application Support/GyazMail (data)/

Mailsmith

MailSmith stores it's data in ~/Documents/Mailsmith User Data/

To store you email in an encrypted location you can make an alias (ln -s ORIGINAL DESTINATION - eg. ln -s ~/Library/Mail /Volumes/EncrypedImage/) onto an encrypted disk image made using Disk Utility if you'd like. Just ensure that the disk image is available or you'll find the data is being stored in a folder at /Volumes/EncryptedImage instead of actually on the image.

Alternatively you could use FileVault that will encrypt your entire home folder. However if the messages are sitting on a server somewhere (eg. not removed by a POP account or using an IMAP account) then the messages are still available unencrypted on the mail server.