what does this mean??

[Caleb]

Account: 'mail.peakrentals.com', Server: 'mail.peakrentals.com', Protocol:
POP3, Server Response: '-ERR Invalid command.', Port: 110, Secure(SSL): No,
Server Error: 0x800CCC90, Error Number: 0x800CCC18

 

[Gary VanderMolen \(MVP\)]

It means you have enabled an option the server does not support.
Go to Tools, Accounts, select that mail account, Properties, Servers.
Make sure that "Log on using Secure Password Authentication" is not enabled.