TIdPOP3 and TIdPOP3Server have been updated to support mailbox sizes larger than 2 GB.
The TIdPOP3.RetrieveMailBoxSize() and TIdPOP3Server.RetrieveStats() methods now return MailBoxSize values using Int64 instead of Integer.
The TIdPOP3Server.OnStat event handler now receives its oSize parameter value using Int64 instead of Integer.
As these are interface changes, you will have to update your code accordingly.