MailStore Home cannot export plain text files, as this would not archive unmanipulated email-data. Only export to servers, applications like Outlook or Thunderbird, and to message file types like pst or single eml-/msg-files is available. However, if you find a way to import single eml-/msg-files into your database, the rest of the process can be achieved with the export of search folders.
But, at this point, I need to warn you that "sales database" hints to a violation of the general terms and conditions. MailStore Home is for private use only.