Is it possible to use chilkat IMAP.FetchSingle asynchronously with multiple threads?
I don't know how to answer this without knowing your programming language.
There is no async method for Chilkat IMAP (at the time of this writing, which is 14-Feb-2014). However, the Chilkat classes/objects are thread-safe, and for programming languages where you have the ability to create a thread, nothing should prevent you from creating a thread and calling FetchSingle synchronously in the background thread -- effectively making it an asynchronous call where your foreground thread is free to do other tasks while FetchSingle is downloading the email.
Even if Chilkat provided an async method -- the meaning of asynchronous is simply that the task runs in a background thread freeing your main thread to handle other things, such as the user interface. It does not provide the ability to do multiple IMAP commands in the same session at once.