I am no expert but the TaskTask Manual (accessed from the iPhone app ) seems to contradict what you are saying, and that Basic or NTLM are supported, but Negotiate is not supported.
Originally Posted by hwinter
"For Exchange 2007 and Exchange 2010 Servers:
For automatic account configuration, autodiscover published using the DNS naming scheme (autodiscover.yourdomain.com)
Exchange Web Services enabled and published (if not using autodiscover, it must be published in the default virtual directory, /ews)
Authentication: Basic (plain text) or Windows Integrated Authentication (NTLM)
With Exchange 2010: Some servers are configured to only support “Negotiate” auth. TaskTask is not compatible with this setting and requires either Basic or NTLM authentication to be specifically enabled."
I have used TaskTask for a while now on my company's Exchange 2007 system and Exchange 2003 before that. One of the features I like is the support of Task Folders, which is also supported in the Reminders native app ( iPhone 4S IOS 6.1 ).
Tags for this Thread