Maulik has given you a good start. What you need to think about are the practical difference between the two options. The clear difference is "get". So what does "get + past participle" give us?
Well, firstly, movies don't release themselves! But I think you knew that. So our second option is not great, as we can't use "release" as an action of the movie itself. For this to work we would need a verb that can be something that a movie does.
If a movie doesn't suck.
Moving on to "get", in your first sentence; this sentence is perfect - it sounds natural and is entirely self-explanatory. "Get" is an extremely flexible verb with many uses and meanings. Its function in this case is to externalise the action. That is, we are saying that the action "occurred" without explaining how, and more importantly by who. This is a form of the passive/causative, which is a vital tool in English.
We use "get + past participle" to externalise an action where the "agent" (who did it) is unknown, unimportant, or self-explanatory.
Here are a couple of other examples:
When a book gets published, it is a nervy time for the author...
If you get arrested, it's important to know your rights...
In the event that you want to explain who performed this "externalised action", you can do so by simply using "by":
If a movie doesn't get released by a movie company, it's likely due to...
Have can be an auxillary verb, but get cannot.
To have {noun} means to possess something. The "something" can be a physical object, a physical or mental state, or an outcome.
To have {infinitive} means to be required to do something. It can mean "being forced to" in the sense of that there will be negative consequences if you don't do it. It does not necessarily mean you were held at gunpoint and coerced into doing something.
To have {past participle} is an expression of a perfect tense (past, present or future depending on whether it's had, have/has, or will have). Have used this way does not mean anything in and of itself, it's an auxillary verb and cannot really be substituted with another verb.
To get {noun} means to acquire something. The "something" can be a physical object, a physical or mental state, or an outcome. I worked today and got $200; Today I got sick. Today I got my bills paid off. It may also be used in place where have can be used when the subject is emphasizing that he/she is bringing resources to an event - i.e. acquiring resources for the event. This is a nice party. I got a case of beer.
To get {infinitive} means to be allowed to do something. I get to go to the park.
To get {past participle} means to do something to become a certain state. I got cleaned up. She was unlucky and got screwed.
So, I hope that clears up any confusion you had about the meanings of have and got.
Now, with the above in mind:
I have got this car.
Gotten is the proper past participle of get and is what should be said here, but the above is common (so common that I can't remember the last time I heard I've gotten this car.)
So I have got(ten) this car means I have acquired this car. It's to get expressed in the present perfect tense. Of course, if the person saying this is talking among a group of friends, he/she telling them basically the equivalent of I have acquired this car for us, even though it would also make sense to say I have this car.
This:
I have got to go now.
is breaking the rules, but not uncommon, at least in my location. I gotta go is a way to write the quickly-spoken form of this (but isn't a real word). Avoid using it in a situation where you are expected to appear/sound educated or in writing.
Consider to have got {infinitive} to be a phrase of it's own, and this means the same as to have {infinitive} but stronger. Also don't get it confused with the past tense of to get {infinitive} above.
And, as this says, in American English, have got to is ONLY used in the simple present tense.
Best Answer
have somebody do something means that you arrange for somebody to do something. Here are some examples.
It does not imply let or make. get somebody to do something generally means persuade somebody to do something:
get somebody in to... has a roughly equivalent meaning, but could only be used when employing somebody, most likely on a short term basis, for example a builder:
Regarding your two sentences, the first one suggests that you normally or habitually arrange for him to deliver the letters, or you have arranged that he will normally or habitually deliver the letters. For example you might be talking about a member of staff who is responsible for delivering all of the mail on a daily basis.
The second one means that you recently arranged for him to deliver a particular collection of letters, and he is doing it right now.