Are there any cross-platform (only interested in Windows and OS X) IMAP libraries which I can use from C++? Preferably open source as well.
I am currently using the IMAP library from Chilkat, but this is Windows only.
I've found libEtPan and VMime and just wondered if there were any others I could look at to compare.
Another good choice can be cURL library which is C library but it has C++ bindings - cURLpp.
The best thing is that it is licensed under the MIT license which perfectly fits for the commercial use or a non-opensource projects.
Although a bit dated since it's development has stopped being open-source, you can check the UW-IMAP toolkit. However, its primary author continues development of the toolkit under the name Panda-IMAP and makes it available to anyone who wishes to donate for the development of the project.
What about VMIME?
It has all my favorite things in a library:
Other alternatives are libetpan (a C language library) and Mailcore (a C++ wrapper for libetpan)