Your thank-you email after the interview should be honest and sympathetic. Obtrusiveness in particular can damage a good impression, which you actually want to underline with your letter. Therefore, please refrain from making any demands in the message. Don’t tell your contact person that they have to make a decision about you or that they should speed up the decision-making process.
You shouldn’t sound too chummy either. A friendly thank you is enough. If you sound like you’re trying to score brownie points, your contact person will notice and may take it negatively. Rejection of both your message and your whole application would be the most likely outcome.
Anyway, you have to be brief. Under no circumstances should you provide an excessively long letter of thanks for additional work. You can assume that the personnel managers have a lot to do during the application phase anyway. If they then have to work their way through an overflowing email, this will certainly not create a good atmosphere. With a few friendly sentences, on the other hand, you can improve your mood and collect bonus points.
In order to be able to thank you at the right place, you should first find out the correct contact details of your contact person. Especially when it comes to e-mail traffic, communication usually takes place through a personnel department general address. Therefore, use the conversation on site and ask for a business card at the end. In this way, you can reach the right person directly.
Also, don’t forget that this message is also part of your application. Therefore, the message must be absolutely error-free. Since a thank-you email only covers a few sentences, any spelling, grammar or wording mistakes are very serious.