Occasionally, I accidentally delete an email from an email account - for IMAP accounts this is usually fine, as it just moves them to the deleted items; I appreciate that any action will have to happen prior to the next sync (when the mail will get deleted from the server), but is there any way to recover/cancel deletion of an email for a POP3 mailbox?
It depends entirely on how you have set up POP3. If you have selected "leave a copy on the server" then yes most likely you can recover it - by going straight to the server. There is also an option to by going in to
mail>menu>folders>[show more]>deleted items
But that option I think you may have to set up. I would always recommend you use IMAP for reasons such as this.