Desktop Mail unable to connect - Laptop Mail works fine

My Apple mail from my iMac desktop to a hosted server email account (JustHost) suddenly stopped working for the two different accounts I use earlier this week. Mail set up for my AirMac laptop continues to work fine, as does my iPhone and iPad.

I've confirmed that the settings for the desktop are identical to the laptop yet I still get a "Trying to log into this SMTP account failed. Verify that the username and password are correct."

Any ideas?

J. Mike