I know that using * in IMAP FETCH Command either defines all or one mail but does "*:*" also defines all mails in the selected folder? Does it defines something else too? Asking cause my company is implementing its own IMAP server, and I couldn't find any reference to *:* in the RFC 3501 and 4466.
If possible, please also cite the RFC.
* does not mean all mail. As a number, * means "the last message in the folder". More generally, 42 means "message 42", 42:50 means "messages 42 to 50 inclusive", 42:* "messages 42 to the last one", and * means "the last message", see? *:* is another way to say "just the last message".
But *.* doesn't mean anything in particular. I can't think of any case where that is even syntactically valid.