Is it possible to use multiple accounts from one email address in K9 application? In the company I work for We would like to use one general email address, but different accounts. Is it possible to do that?
AFAIK, it's not possible (Related How to setup K9 Mail properly for free email services offering multiple aliases for same email box?)

K9 mail isn't really active in development and I would rather suggest you switch to a modern Email Client which does this and much more. I am talking of FairEmail. Don't be discouraged by "unreleased"  status. It's very much functional and actively developed. See this XDA thread.

Specific to your query see FAQ 9

I am not associated with the app but would happily recommend this being a better alternative to K9 mail - it's leagues ahead of K9