IMAP is a commonly-used connection type for syncing mobile devices of all shapes and sizes with email addresses. However, IMAP can be handled differently by different mobile device manufacturers, much less mobile device operating systems.
A perfect example of this is how IMAP on Android devices doesn't support viewing, much less accepting or rejecting, calendar invitations for most major email systems. By all accounts, Android simply disregards calendar / event notifications and invitations when using IMAP. This happens regardless of the mail server being used. Therefore, this IS NOT a SmarterMail issue, but revolves around how Android clients handle IMAP requests and standard calendar invitation formats. For more information, see https://code.google.com/p/android/issues/detail?id=26109