There is nothing that is similar between Outlook and Thunderbird in mail/contact storage. By default Thunderbird keeps the profile data (not the program itself) within the computer 'User Account' as the user account logon acts as first line defence from prying eyes. So in Windows OS, this would be here: C://Users/<User Account name>/Appdata/Roaming/Thunderbird/<profile name> For backup purposes you would copy the 'Thunderbird' folder - see image below. Each 'profile name' folder typically has this construction : 123abc4d.default Each 'profile name' folder contains all the various files and folders required and can contain all your mail accounts, emails, filters and contacts, but not in the same files. Image below is a typical example showing contents of a 'profile name' folder. Address books are stored in *.sqlite files in the 'profile name' folder. The 'Mail' folder contains all POP account name folders and also the 'Local Folders' mail account. The 'Local Folders' mail account is a special mail account created by default and can be used for mail storage which is separate from any mail account. Eg: if imap account needed to increase server quota, emails could be copied to 'Local Folders' before being deleted off server. The 'ImapMail' folder contains all the imap account name folders. All fully downloaded emails are stored in mbox files (they do not have any extension), so each folder eg: Inbox, Sent etc will have it's own mbox file. The mbox files are a text file and emails are written to that file in the order downloaded. Image below showing typical contents of a mail account name folder - ignore the info on ImportExportTools as I used image for another purpose. If you use IMAP mail accounts then they can be created on each computer to hook up directly with mail server. Imap accounts store emails on server and are designed to show a view of what is stored on server. This means you can view via any computer or via webmail and see the same mail account data. Imap accounts are the best method when using more than one access point/computer/phone etc. There is no need to download to a separate server-like computer and access via shared files type method. The profile name folder can be stored in any location on computer eg: different disk drive. Some people have managed to use on NAS drives and cloud etc but it does seem to have less issues if profile is on same computer. Thunderbird also uses a profile per installation policy which means a profile able to run on version eg: 78.11.0 cannot automatically run on an older version. So if profile was not on computer - file share - you would need to make sure that all computers running Thunderbird would need to be updated to identical version prior to starting up any version on any other computer. Helpful info: http://kb.mozillazine.org/Profile_folder_-_Thunderbird https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data http://kb.mozillazine.org/Sharing_profiles_-_mail http://kb.mozillazine.org/Sharing_a_profile_between_Windows_and_Linux