Working for a japanese company, I asked a japanese colleague about what to use, other than
-san.
"Westerners will get away with using Mr. or -san", he said.
He addresses his superior using -dono, while his superior addresses him using -kun.
Visiting dignitaries of other companies justify the use of -sama, which you would not use within the company itself.
When talking to top-ranking company officials, it is also possible to use the title (i.e. the japanese form of director) as a honorific.
A lesson my colleague taught me is the following :
"When communication with japanese, use -san. If you have something important to ask for, use -dono."