Old emails keep resending by themselves

I have sent an email with attachments to a contact, but the email keeps resending itself every week or so. This is happening a lot to a range of contacts.

It may be that the email is stuck in the Outbox, though it would then probably be resending continuously. But check the Outbox for your account and for Local Folders. If you can’t see the Local Folders, you can enable them in Menu > Tools > Settings > General > Show Local Folders.