Question regarding the Outbox in the default Mail app on the iPhone

Hi everybody
I'm using the default Mail app on my iPhone 6S running IOS 10.2 1 and liked it a lot, but where can I find the Outbox? I have 4 unsend messages I would like to remove, but under Mailboxes, under TelkomSa I can find all the other folders except the Outbox. Is there perhaps another way to remove unsend messages apart from deleting the Mail account and reinstall it again? I use an imap account. I have only one mail account installed.