Working in a Japanese based company I often see that in written English which is (directly or indirectly) addressed to Japanese the suffix -san is attached to names.
With some basic knowledge of Japanese I have some understanding how -さん is used in Japanese. Having in mind that it would seem unnatural for me to encounter Herr Müller instead of Mr. Müller in an English text I am wondering how natural it is for a Japanese to see -san being used in an English conversation a) attached to a (romanized) Japanese name or b) attached to an English/German/... name.
I hope this question will not be marked as opinion-based because I am actually interested in a general answer to help improve my conversation with Japanese people.