Function imap_key_without_words 

pub fn imap_key_without_words(
    search: &Search,
    account: &str,
    folder: &Folder,
) -> Option<ImapKey>

The same without words, for a server that refused them: the days, the sizes and the marks asked, the rest checked here. GreenMail, for one, reads FROM as a whole address and refuses a part of one (“@bank.example”).