|Just a clarification to avoid any confusion:|
incoming mail(POP3) : <get this from your ISP - It may be on their support pages>
outgoing mail(SMTP) : <get this from your ISP - It may be on their support pages>
This may or may not be your ISP. Not all ISPs provide Email facilities and if you are using something like Hotmail or Gmail then your ISP wont be able to help.
It would be more accurate to say your Email provider, whoever that may be.
Once you have set everything setup you should be able to retrieve mails sent to you as they will probably still be stored on the Email server. Depends how you configured your Email client, to keep mail on server or to delete or delete after a period of time If you never set the configuration it usually defaults to keep.
Mail you have sent is probably lost forever.