When mail is retrieved using POP3, the displayed mail counter is different from what the browser displays

I have been assigned an email client that accesses mail from a Yahoo POP3 server. After spending several days, I successfully made an email client. My application correctly retrieves mail from the POP3 server and sends mail to the SMTP server.
Problem in; the application can only receive letters that have a received date within 60 ~ 70 days (I'm not sure about the number of days).
When I checked the account in the browser, I can see all the letters, but when I receive mail from my mail client, it only receives mail received within 60 ~ 70 days. Also, when I used OpenSSL to check mail, the mail count shown with the openSSL client is the same as for my application.
I wanted to know if this behavior is Yahoo! Pop3 or is it the same for all other postal service providers. It would be very helpful if someone could provide me with a link to a URL that shows that you cannot receive mail from POP3 when the received mail date is 60 ~ 90 days (or some limit).