outlook 2007 can’t send/receive pop3 email in window XP

I have a user who can’t send or receive outlook 2007 email in Window XP.

I had re-installed outlook since it was running slow. I removed all add-ins, RSS reader to enable outlook to run fast. All the pop3 & SMTP server addresses are corrected. Username & password are corrected.

When I test the email account, it ask for security certificate. Outlook couldn’t send email thus it changed to non-encrypted method of setup. Email test was successful.
however, I sent a test email but it hasn’t come back. There is no error during email account test.

What is going on?