Try this first:
Go to Tools, Accounts, select that mail account, Properties, Servers.
Make sure that "Log on using Secure Password Authentication" is not enabled.
If the problem continues, is your Yahoo account a free one or a paid one?
If free, is it a US-based account? If not, which country?
Gary VanderMolen, Microsoft MVP (Mail)
"apm" wrote in message
Account: 'pop.mail.yahoo.com', Server: 'pop.mail.yahoo.com', Protocol: POP3,
Server Response: '-ERR popgate unknown command', Port: 110, Secure(SSL): No,
Server Error: 0x800CCC90, Error Number: 0x800CCC18
>> Stay informed about: When opening my mail