„Ich kann die E-Mail öffnen nicht.“ Wrong

Question

I had understood that to negate an entire sentence, then „nicht“ should be placed at the very end of that sentence. However, „Ich kann die E-Mail öffnen nicht” has been marked incorrect, and I am told that it should be, „Ich kann die E-Mail nicht öffnen.“ Could someone please explain the logic or rule here? Why does “place “nicht” at the end” not apply? Thanks.

Answer 1

I had understood that to negate an entire sentence, then „nicht“ should be placed at the very end of that sentence.

Someone told you a wrong rule. Forget it immediately.

Negation in German is very simple. Put nicht in front of the item you want to negate. That's the rule. Let's negate different items:

Du weißt, dass ich die E-Mail öffnen kann.

Du weißt, dass nicht ich die E-Mail öffnen kann. (but someone else can open it)

Du weißt, dass ich nicht die E-Mail öffnen kann. (but I can open something else)

Du weißt, dass ich die E-Mail nicht öffnen kann. (but I can do other things with it)

Very simple. However, there's a small quirk. It's that darned V2 rule. In main clauses, as the last word order rule applied, the conjugated verb is moved from the very end to second position.

Du weißt, dass ich die E-Mail öffnen kann.

Ich kann die E-Mail öffnen.

See how kann was moved from the very end to second position? And that's the only thing that moves. All the other stuff works just the same in the main clause:

Nicht ich kann die E-Mail öffnen. (but someone else can open it)

Ich kann nicht die E-Mail öffnen. (but I can open something else)

Ich kann die E-Mail nicht öffnen. (but I can do other things with it)

Because of that V2 rule being the last word order rule applied, in some corner cases nicht ends up lonely at the end.

Du weißt, dass ich die E-Mail nicht öffne.

Ich öffne die E-Mail nicht.

But that's only a by-product of the V2 rule.

Answer 2

Sort of different answer than what Janka already provided, it may help different types of learners.
The negation appears to the left of its focus - but only if possible.
Have you learned about the field model of the german sentence?
The second position can never have anything else than the finite verb.
So in

[Ich] [öffne] [die E-Mail].
First Second Middle

you can't put "nicht" in front of "öffne".
So it ends up in the middle field.
The middle field has a very precise ordering of all the things that can be there, of all types of Objects, adverbials and particles. These (not strict) rules tell us that

Ich öffne die E-Mail nicht.
Ich öffne nicht die E-Mail.

both have the same value of negation. However, the second one could be confused with negating only "die E-Mail", as it is to the left of it.
So it is put to the end. Because again, the second position does not allow for the negation to be at its position.

In sentences with the verb at "first position", it is actually considered to be at second position but with the first empty. That is why in those, just as well, "nicht" stays in the middle field.

Mache ich das nicht?

The rules of middle field positioning tell us that objects that are pronouns usually stand in front of the negation particle, so

Mache ich nicht das?

is NOT used.
However, objects that are not pronouns allow for both:

Mache ich nicht den Abwasch? Mache ich den Abwasch nicht?

Again, there is confusion possible, so the one at the end is used.