@skippystarr
The mail account in your profile? That's IMAP (by default).
Are you deleting messages by "move to deleted" (the trash can icon)?
And they come back after you check mail in the account?
Please check / fix the mapping of the app's "special" folders to server folders:
- Long press the account
- Options and folders
- Folders
Let it refresh
- Find the Sent folder (the name varies by mail provider, may be "Sent Items", "Sent Messages), choose "Sync with [ Sent ]".
- Repeat for Deleted and Drafts