Thank you for writing to Aspose support team.
I have investigated this issue with the latest version of Aspose.Email for .NET and was able to observe the exception as you have mentioned. It has been further logged as NETWORKNET-34495 in our issue tracking system for further investigation by our development team. Once there is some information available in this regard, we’ll update you here via this thread.
Aspose.Email for .NET 4.6.0 is planned to be released during the first week of Oct 2014. We’ll notify you here via this thread once the fix version is available for download.