Order in MessageInfoCollection

Both ImapClient and ExchangeClient give me a messageInfoCollection. I am wondering whether that collection has any particular order or user can set it up.

For example, I got 50 emails using ListMessages(50). Are these 50 emails the oldest, newest emails in the mailbox folder? Or they are the first 50 emails sorted by subject, from? Or they are just randomly picked in this mailbox folder? Thanks.