It happens, when we forgot our email passwords after sometime configuring your email accounts in pop3 email client, as the most of the application like ftp clients, pop3 client offers the feature to remember the password.
Just as all these applications offer to remember passwords which makes us lazy and set the option to remember it. Now, the main problem occurs when you may need to reconfigure these type of application some where else or on the same system for any reason.
SinffPass is small nifty freeware by Nirsoft which comes to rescue in these type of situation. It listens to your network and capture the passwords that pass through your network adapter.