Daylite itself has no control over which account Apple Mail chooses to send an e-mail as this is being controlled by Apple Mail itself. By default Apple Mail selects the "best account" automatically, which means that Apple Mail utilizes the mailbox that is currently open in the Apple Mail app.
You can, however, change this behavior in the Apple Mail Settings and define the desired mail account as default. This default account will then be used when sending e-mails from within Daylite.
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