Hi @Cindy Coppens ,
Thanks for posting in our Q&A forum.
In order to have items sent from different email accounts saved to a single folder, you could create a rule to accomplish that in each of the secondary <Sent Items> folders.
1.create a new rule for each of the applicable Exchange accounts you want this to apply to
2.select <Apply rule to messages I send>
3.select <through the specified account>
4.next, select <move a copy to the specified folder
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