Most e-mail programs let you choose how often the program should check for new messages in a POP mailbox.
If you use this feature, we recommend that you check for new mail no more often than once every two minutes. You certainly shouldn't set it to check more than once per minute; if you do so, some connections may be rejected to limit the load on our mail servers.
If you receive large amounts of e-mail and need to check more than once every two minutes, we suggest using IMAP connections instead. Mail programs that use IMAP make a single persistent connection (instead of many small connections), and cause less load on our servers.