1- Understanding: While it might seem that they are very misunderstanding, this is not a war to fight fire with fire. If they are jealous then you need to be understanding not only of the situation, but of the reasons that would cause their jealousy in order to avoid them or help them get over it. The past could be one of the main reasons why your partner is jealous. Lack of confidence is one of the reasons that contribute directly to jealousy.
2- Timing: You have to be careful when you bring up something that would enrage them. If you are going to tell them about a person who tried to flirt with you at a time close to their birthday or your anniversary then don't blame anyone but yourself for the stress you are going to be in until it passes. While you would argue that you should tell them whatever you want at any given moment, you wouldn't like to know that you failed to pass a job interview on your birthday because it would ruin it. Consider this adding insult to injury.
3- Reasoning: The biggest problem with jealous people is that they are misunderstood and mistreated. If you had an experience that you would want to forget about, you would do anything to avoid it and when it comes up at any occasion, you will get upset. If your partner has gone through an experience that they have not told you about where it ignited the jealousy in them then you wouldn't really know, yet you'd have to handle it in a similar manner to the way they hid it in the first place. Instead of giving your partner a reason to be jealous, give them a reason to trust you. Show them that your faith to them will not fade no matter what happens. The process for someone to be less jealous can be a long tiring one. You would have to bring all your weapons in order to win this and you would have to be patient. If you are not then don't expect anything to come out of this because you will get mad at your partner and that would immediately make them think that they had a righteous place for their jealousy. All you need to do is to prove them wrong a few times and then they will be calm and they will trust you even more. The biggest problem with jealous people is that they don't have much trust or faith in anyone and they expect everyone to betray them.