Type: boolean
Default: unset
This variable controls how copies of outgoing messages are saved. When set, a check is made to see if a mailbox specified by the recipient address exists (this is done by searching for a mailbox in the folder directory with the username part of the recipient address). If the mailbox exists, the outgoing message will be saved to that mailbox, otherwise the message is saved to the record mailbox.
Also see the $force_name variable.