I'm a veteran programmer in Delphi with more of 15 years of experience. I have worked practically with all delphi versions, at present I use Delphi XE7.
I read your document and understood perfectly what do you want , your requirements are explained very well. I downloaded and reviewed the old software too.
I have developed many software where I have used threads and the Indy components of Delphi. Indy packet has components as TidSMTP, TidIMAP4 and TidPOP3 which allow to develop a client of email very efficiently. The requirements of the software have difficulty but I can do it because I have many experience in this kind of work .
I defined a milestone but this is provisional, if you are interested in my offer, we can discuss about the milestones according to your priorities and definitions.
Regards,
Mel