Sometimes I delete e-mails in my inbox by accident. As my e-mail is an open internet account (gmail, hotmail etc.) the deleted e-mails are irretrievable. Is there any way, I can develop a tool that can help me in getting back the emails I delete?

Nomally after you delete your e-mails they will appear in trash box, if you want to communicate/manage your mailbox you must learn about IMAP protocol and your provider must open IMAP protocol for your tools also.