At this time my interest in your tool (Windows and Unix) is to be able to access MS Exchange servers, ie users mail and calendaring. Same interest regarding Lotus Notes/Domino servers.
What issues, if any are involved in accessing exchange mail servers using your API's and possibly with Lotus notes/domino? I don't know if there are any bottlenecks considering both tend to be proprietary.
The requirement is to be able to handle the sending/receiving/viewing of mail and possibly calendaring for both using a proprietary client on an obscure system (although through a windows/unix/linux) server.
There should be no difference. If a server properly implements the server-side of the POP3, IMAP, and SMTP protocols, then a properly implemented client-side can communicate with the server.
Calendaring is not a function handled by POP3 or IMAP, so it is not explicitly handled by Chilkat. (Unless calendaring messages are simply emails that contains information in some format, in which case your app would be responsible for forming the email for calendar updates, or reading calendar information from an email.)