Darren: Yes, the Default setting is 1
week and you don't like it. So change it to Never.
My hubby accidentally deleted a Proposal. Bc his Mac techie set his iPad Mini up (a talented guy but my hubby refused to wait for me to use the Mac techie, an Apple Beta tester, who has been setting up all my devices for years). When I went to my own iPhone which my Mac Wizard synched with all my other 5 devices: 3 iPhones. 2 iPads, a Mac laptop and the desktop, the Wizard KNOWS to change those kinds of silly things Apple does, my own Mail Trash accounts are set to Never delete.
Best of all, there's always AppleCare support if you invested in it as we always do for the maximum allowable period, a Senior Tech Advisor took over the call and case: Apple was able to RESTORE almost all of his Sent emails which had disappeared for no reason. He got back 97 of Proposals, spanning more than 1 year. The emailed Proposol was NOT among them but I knew enough about iOS to go into Advanced Settings to check on what was the time limit on Deleted emails. Sure enough, the techie he used left it in Default (Mac Wizard would have known my hubby's tech skills are poor and would have safeguarded us by changing the Delete settings to Never). My other devices are all set to Never after being in the Mac Wizard's hands for syncing a few months ago. If you call Apple in Cupertino, you usually get better service (fewer mistakes) than making a Genius Bar appointment. If you have a problem communicating with a particular CSR, politely hang up and call back for another one. With Apple, there is usually more than 1 way to solve any problem. One must simply exercise patience and courtesy. Best of luck.