Thank you emails: What a thing. Do people actually want to receive these? What is the point? Conversely: Why wouldn't you write a thank you email?
Thank you emails work. They work in their specific, niche circumstances where you are teetering on the edge of getting a job. If the company already has a preferred candidate or there was something acutely flawed about your candidacy, then no amount of flowery prose is going to save the opportunity. But...in those times where maybe you are the best they've seen so far or an intangible personality trait makes you an esoteric but exciting choice, a well written and targeted email can make the difference.
Each email needs to have a specific objective. That objective can be to repair some damage done during the interview (perhaps a gaffe or brain fart), display curiosity, or just show that you are an appreciative person who doesn't take things for granted.
First thing: As I wrote in How to Work your Recruiter - know who you are interviewing with before the onsite. Ask your recruiter for the emails of those folks before you arrive onsite. It will come in handy later.
Second thing: When possible, write the email as if you are already on the team. "Im really excited for when we release the X product feature." or "I can see us moving into a new vertical in a few years". This is an old sales tactic and puts you on the team psychologically. Actually, it's useful to talk like this too during the interview. Put on the company hat, see how it feels! Talk like you are already there; on the team.
Alright, the first scenario: You fucked it up. This is rough. You messed up an interview. Later on, you realize you gave the wrong answer or didn't understand what they said. Or perhaps you were defensive about something and the conversation got stilted. This is definitely doing to come up on the debrief so your goal is to get an email out to that person ASAP and explain yourself. If it gets there after the debrief it doesn't matter. This is where having the emails really helps.
You are going to be writing this email quickly, so make sure you are grounded and check the email for voice. You need to be calm and collected. Objective and matter of fact. Any sort of anxious energy and you should just not write the email.
Thank the person first for the interview, then say what you observed and what you think may have been happening in the interview. Take lots of blame. This was all on you (even if it wasn't). Then restate whatever it is you wanted them to hear in the first place. Cross your fingers. If you did this right, the content of your email will now also come up in the debrief. Its like you are right there getting to set the record straight!
Next, this is ideal for any hiring manager or decision maker that you met and had some rapport with: Thank them; Then, Ask some follow up questions. Not a lot, but maybe one or two. The questions need to be authentic and tied to the conversation you had with them. Even if you really want the job badly, think about why maybe you don't want the job and ask some pointed and polite questions on those topics. What happens if the next funding doesn't come through? Do you see this job having any adjacent leadership opportunities coming up? You said the goal was X, what happens if we hit Y?
Finally, if you just had a casual chat with the boss's boss or the CEO or a Founder and you don't have any specific follow up, just thank them. Tell them you appreciate them taking the time and you really enjoyed hearing about X and that you are excited about the opportunity to work together. That's all.
Again, you could be saying all the right We's and getting all the right notes out to all the right people and if your candidacy is off the mark or you are second in line, it's just not going to change the outcome. But when you are stretching for something, most of the time you are going to come up short and sometimes that right note can make the difference between just short and just right.
Oh, and when should you not send a thank you letter? Hey, if the job isn't your jam or your #1 opportunity just came back and want to offer you: Honestly, don't bother. This is a recruitment process. Both parties have to be in it for any of it to be worth anyone's time. Even a nice note is a waste of time and eye balls if you are no longer considering the company. Stand down. Let the next person have their share of attention. Enjoy your new job!