How did letters of introduction work?

Back before the printing press, and even somewhat after, how did letters of introduction work? Yes, you’re carrying a document that says that you are X and Y makes certain statements about you, but when you present yourself at Castle A, do you give your letter of introduction - which is priceless to you- to the gate guard? Or what?

IIRC from my reading, you might show the seal to the guard, to get you inside, then you gave the letter to the intended recipient.

You would first make an appointment with the person in question to present your letters of introduction. They would tell the guard or doorman that you would be coming at an appointed time. When you arrived you would present your card to the guard and/or doorman who would escort you into usually the major domo to whom you would present your letters of introduction.

At this point you would either return to your apartments or if the letters of introduction are short and to the point you would wait in the sitting room. Once the person has read the letters they would either send for you at your apartments or send for you in the setting room and you would meet with the individual and discuss any common ground.

One was was for A to know B in the city where C was going to go. A then gave C a letter vouching to B for C’s reliability. B then became C’s sponsor in the new city.

Well yes, but did you surrender your letter at any time? If you did, would it not have been inconvenient - to say the least - had it been kept or destroyed.

Well, you give it to the person who it’s for. Lets say it’s the middle ages, and I’m in Paris, and I want to go to Antwerp. So my friend says, “Hey, you’re going to Antwerp but you don’t know anybody there? My good friend Quartz lives in Antwerp. Let me write him a letter for you.”

So then, our mutual friend writes,

So, then when I get to Antwerp, I give you the letter, you read it, and know that your friend Jacques vouches for me, and so you help me out.

Just be careful if your creepy Danish uncle sends you and your two buddies to England with a letter of introduction.

Hey, I’ve actually used a letter of introduction! In a place where phones are sketchy and bad roads make transport and mail unreliable, they are still the perferred way to introduce yourself to local dignitaries.

You just give it to the person it’s intended for. If they are not available to meet immediately, you give it to their secretary/underling/whatever.

You assume that whoever you are giving the letter to is not going to destroy it because they are usually someone in a public office of some sort and presumably did not get there doing wonton acts of random spite like that.

As a followup, was there usually anything in letters of introduction for verification purpose? For instance, your friend Jacques might say something about you in the letter that Quartz can use to check that you’re really the person that the letter was written about.

Since the letters are clearly important and valuable, I don’t imagine that they’d be swiped easily… but heck, maybe you were attacked and killed on the road to Antwerp, and the letter was sold to someone who wanted to use it in your place.