[Exchange] Sent messages in wrong "Sent" folder

When using an MS Exchange user (me@test.com) with access to other accounts (it@test.com), mails sent from that other accounts don’t land in that accounts “Sent” folder, but in the root users “Sent” folder.

How to reproduce (eM Client v.8 and v.9):

  1. Set up an Exchange user that has access to other accounts mailboxes. (me@test.com)
  2. In the Exchange users account settings, select the “Exchange Web Services” Tab
  3. Add the other accounts mailbox, your account has access to in “Delegation” > “Accounts you can see” > “Show” (it@test.com)
  4. Save and quit the account settings. In your eM Client mail view, you can see the additional account below your own.
  5. Compose a new email and set the additional account as sender. (it@test.com)
  6. The sent message doesn’t appear under the additional account’s sent folder (it@test.com), but in your own (me@test.com).

This doesn’t happen in for example outlook, where the e-mail correctly lands in the Sent folder of the mail account who sent the message.

Does someone have a tip in how to fix this or is this a bug?