A user deleted the "Drafts" and "SentMail" folders in his mailbox.
I have recreated the folders using the following commands in the backend:
doveadm mailbox create -u user@domain.com "Drafts"
doveadm mailbox create -u user@domain.com "SentMail"
and also subscribed those folders in OX Webmail IMAP Folder Subscription.
But those folders are not serving their purpose. Instead, OX considers those folders as normal: