In regards to a question that you answered about somone recieving oral sex and then noticing a sore on his penis. Why did you say he is at risk? From what I understand this would still be essentially a saliva to blood contact. That would be like saying that if you had a sore in your mouth and you deep kissed somone that you should get tested? I know things are theoretically possible but if something like this has never happened in the past ( from what I gather from this site and others there have been NO reported cases) then I do not see why you told this person to get tested. I have heard that recieving oral sex does not even constitute the need for a test. I know that people can't say 100 risk free because there is not many things in life that are, but if a bridge has a small crack in it I would not tell every car that drives over it that it might colapse!!!!!!!!
STDs in general can indeed be transmitted through oral sex. The person who sent the original message had noted a sore on his penis afterwards, which could have facilitated transmission. Transmission of HIV through oral sex can happen if the recipient has minute breaks in the inside covering of the mouth, where virus can come into contact with the recipient's blood. A recent study from San Francisco suggested (but did not prove) that oral sex is responsible for less than 10% of HIV transmission between gay men. I hope that makes my original answer clearer.