Right-click on your Office 365 account and select “Subscribe…” from the drop-down menu.
Place a checkmark next to each of these folders: Drafts, Deleted Items, Sent Items.
Click Subscribe button, then click OK.
Right-click on your Office 365 account again and select “Settings…” from the drop-down menu.
Under your Office 365 account, select “Server Settings.”
Within ‘Server Settings > When I delete a message’ section, select “Move it to this folder” and from the drop-down, select Deleted Items.
Under your Office 365 account, go to “Copies & Folders.”
In ‘When sending messages, automatically > Place a copy in:’ section, select “Other” and use the drop-down to select: email@example.com > Sent Items.
Under the “Drafts & Templates” section, select “Other” and make sure it states Drafts on firstname.lastname@example.org.
Click OK and close Thunderbird, then re-open it.