To activate Maildir in Thunderbird

To use folder size > 4 GB in Thunderbird,
You can set mail.serverDefaultStoreContractID = “@mozilla.org/msgstore/maildirstore;1” in tools ->preference -> advanced -> general -> config editor to use berkeleydb for new accounts. [This feature is experimental. so backup data].

Thunderbird preference

configuration editor Thunderbird

 

 

key to change

So next time if you create a new account, storage of mail will be in maildir format.

Default is “@mozilla.org/msgstore/berkeleystore;1”, which is mbox.