Learn English – What’s the difference between “Once I’ve graduated” and “Once I graduate”

I do wonder sometimes at the 'rules' that people get taught for when to use what tense in English. They usually seem to work well for the examples used in teaching, but lead you down a misleading path as you get further into the language.

The perfect aspect, found in the present, past and future aspects, represents actions at are complete at the time of the sentence (past, present or future). It also puts a focus on the results of the action. The progressive aspect is about actions that are ongoing at the time of the sentence. The simple aspect, when the tense is neither perfect nor progressive, expresses fact - either about a specific action or a general or habitual truth.

When you say "I've received a message" you are saying that you have fully received it - you aren't in the process of receiving it - and putting focus on the result, the fact you have the message. In the same situation, you could also say "I received a message", which is a statement of fact without focus on the result, and is the past simple form. You might be meaning to focus on the fact of receiving, rather than on having the message.

Neither tense indicates any 'strength' of result. Neither indicates whether there is a result still ongoing or effective at the time of the sentence. It just focuses the result. There can also be differences of nuance between past simple and present perfect, but that can depend a great deal on the verb in question, and the subject. For example:

I knew the way from home to school.

This says that, at that time, you knew the way - it doesn't suggest you know it now, nor that you don't.

I knew love, once.

This suggests that you no longer know love.

I have known love.

This suggests that at some point you knew love, and may or may not know it now.

What tense to use is a much simpler, and yet more complex matter than a lot of teaching suggests.

There are various parts to this; I'm focusing on only the overall meaning of each (as opposed to, say, the nuance introduced by "just"). So, I can construct a scenario where Example 1 is perfectly correct, but it means something different from Example 2. I'll use a slightly different example to illustrate:

Example 3

My friend: I am going to draw various things. For each drawing, I'll tell you I have done it and I want you to draw the same and then tell me when you're done.

Me: OK

My friend: [scribble scribble scribble] I have drawn a set of keys sitting on a desk

Me: [scribble scribble scribble] OK, I have just drawn the same thing

My friend: [continues onto next drawing]

Example 4

My friend: [Out of the blue holds up a picture he's drawn] Look! I have drawn a set of keys sitting on a desk

Me: Holy crap, that's amazing! I just drew the same thing!

My friend: [stares at my drawing, then me, then back at my drawing, terrified, as if I might be some kind of witch]

It wouldn't be too hard to morph that into something to do with thoughts rather than drawings -- maybe a scenario with a stage magician/mind-reader asking people to think of things and then tell him when they've done it. Doxastic involuntarism aside, I think the comparison works.

But, ignoring that contrived example, with the meaning implied in your context I would not use Example 1. Example 2 is better/idiomatic.