Function act_set 

async fn act_set(
    session: &mut Imap,
    account: &Account,
    folder: &Folder,
    validity: u32,
    uid: &str,
    action: &Action,
) -> Result<(), SyncError>

action on the messages of uid, a UID or a set of them (“4,7:9”), in folder, whose UIDVALIDITY must still be validity.