Messages are disappearing from my Trash
By default, iOS deletes messages permanently after they've been in the Trash for a week. To change this behaviour:
- Open the Settings app.
- Tap Mail.
- In Accounts, tap your Fastmail account. It will be labelled with whatever you typed in for the Description field when you set it up.
- Tap Account, scroll to the bottom and tap Advanced.
- Under Deleted Messages, tap Remove and change the setting from "After one week" to "Never".
- Tap to go back to your Account, then tap Done.