Just a side note. I'm relatively new to Outlook programming but I got
into quite some trouble because of accessing the UserProperties
directly.
I would write:

UserProperties props = MailItem.UserProperties;
try
{
//Use props...
//...
MailItem.Save();
}
finally
{
Marshall.ReleaseCOMObject(props);
Marshall.ReleaseCOMObject(MailItem);
}

On 17 Aug., 16:47, Sandeep K Sandeep
wrote:
I am adding one user property to an email in outlook 2007 using VSTO Addin.