Here are some articles that I found on this (people are welcome to add any others that are useful):

http://www.everythingaccess.com/tutorials.asp?ID=Outlook-Send-E-mail-Without-Security-Warning

http://www.outlookcode.com/article.aspx?id=52

If all else fails:

http://www.google.com/#hl=en&safe=active&q=a+program+is+trying+to+automatically+send+email+ on+your+behalf&aq=f&aqi=g9&oq=&fp=8ec9ea851cee2c5b