Added an exception message when throwing NotSupportedException
Added an exception message when throwing NotSupportedException

eino-makitalo/MailKit,dsbenghe/MailKit,mganss/MailKit,rajeshwarn/MailKit,sstraus/MailKit,FubarDevelopment/MailKit,jamie-dainton/MailKit,nachocove/MailKit,matt2003/MailKit,jstedfast/MailKit