Error: -3259

I'm getting this error when trying to send & retrieve email. My email works on my iPhone and on my Windows laptop (same domain, different account). It's been going on for a month.

"An operation on the server timed out. The server may be down, overloaded, or there may be too much net traffic."

"Could not retrieve mail."

"Error: -3259"

I'm using MS Entourage for Mac 2008, Ver 12.3.6 (130206)

My iMac is running MacOS High Sierra Ver 10.13.6