The ICalendar module hasn't been upgraded in a while, the latest (and only) version has been released two years ago in may 2012.
That would explain why you would probably run into some issues with that module.
Recently I have been working with this module, and I have it working in Mx5 and it has communicated with both office 365 and gmail.
The setting useSSL is a bit confusing, as you can see in the Java code it does not enable SSL. The boolean will enable TLS. So the name of the attribute is incorrect.
That is probably why gmail is not working for you, when using gmail over TLS it requires you to use port 587
If you try a different port for gmail it should work, or by checking the box use SSL you should be able to configure it to authenticate with office 365.
I will also work with our appstore team to make sure that my latest Mx5 version gets published to the appstore.