iOS and Apple mail don’t. Some servers sometimes have the issue of reusing message identifiers and both clients would show the wrong content for the mail. You’d

iOS and Apple mail don’t. Some servers sometimes have the issue of reusing message identifiers and both clients would show the wrong content for the mail. You’d have to force a resync of the whole Mailbox to fix this. Also: A backup of the mailbox would be unaffected by any server-side change.