puzzling issue: recipient prompted for password when replying

[bhwong]

One of our vendors feedback that whenever he attempts to reply our email, his outlook will prompt him to enter a password for our Zimbra server. Any idea why this is happening when he is not even using our Zimbra server to send his email??? (see attached)

image003.jpg

[kruon]

Maybe the sender's email signature contains some image stored on the zimbra users briefcase or something?

"View source" might reveal what is linking to the zimbra server from that mail.