Quando a internet voltar a funcionar, eu vou enviar o relatório.

Yes, voltar literally means to return or to come back, but in the pattern voltar a + infinitive, it means to do something again.

So:

• voltar = to return
• voltar a funcionar = to work again / to start working again

In this sentence, a internet voltar a funcionar means the internet will be working again after an interruption.

A very similar idea in English would be when the internet starts working again.

Because Portuguese normally uses the future subjunctive after quando when the sentence refers to a future event.

Here, the speaker is talking about something that has not happened yet:

• Quando a internet voltar a funcionar... = when the internet works again / when the internet comes back

So this is not a habitual fact like when the internet works. It is a future condition.

A very important pattern is:

• quando + future subjunctive
• se + future subjunctive
• assim que + future subjunctive, in many cases

Examples:

• Quando eu chegar, te ligo.
• Se ele vier, a gente conversa.

In this sentence, voltar is the future subjunctive form.

For many regular -ar verbs, the future subjunctive looks identical to the infinitive.

So with voltar:

• infinitive: voltar
• future subjunctive: voltar

That is why learners often do not notice the mood change at first.

Compare with other verbs where the form changes more clearly:

• fazer → quando eu fizer
• trazer → quando ele trouxer
• ser → quando for

So in your sentence, voltar is not just an infinitive sitting there randomly. It is the correct future subjunctive form.

Because the expression is voltar a + infinitive.

So:

• voltar a funcionar = to function again
• voltar a estudar = to study again
• voltar a tentar = to try again

That a belongs to the verb pattern. It is not an article, and it is not optional in standard usage with this meaning.

Both are correct, but eu vou enviar is much more common in everyday Brazilian Portuguese.

Two common ways to talk about the future are:

• eu vou enviar = periphrastic future, very common in speech
• enviarei = simple future, correct but often more formal, written, or less conversational

So:

• Quando a internet voltar a funcionar, eu vou enviar o relatório. → natural, everyday Brazilian Portuguese
• Quando a internet voltar a funcionar, enviarei o relatório. → also correct, but sounds more formal

A native speaker will usually prefer vou + infinitive in casual conversation.

No, it is not strictly necessary.

Portuguese often drops subject pronouns when the verb already makes the subject clear. So you could say:

• Quando a internet voltar a funcionar, vou enviar o relatório.

That sounds completely natural.

Using eu can add:

• emphasis
• contrast
• clarity

For example, if you want to stress that I will send it, not someone else, then eu is useful.

So both are fine:

• ... eu vou enviar o relatório
• ... vou enviar o relatório

In Brazilian Portuguese, nouns are often used with a definite article more often than in English.

So a internet is very natural.

English often says:

• the internet
• or just internet in some contexts

Portuguese commonly says:

• a internet

You may also sometimes hear internet without the article, but a internet is very common and natural in Brazil.

Because the sentence starts with a subordinate time clause:

• Quando a internet voltar a funcionar

and then comes the main clause:

• eu vou enviar o relatório

In Portuguese, when this kind of clause comes first, a comma is normally used.

So this punctuation helps separate:

• the time condition
• the main action

If you reverse the order, the comma is often not needed:

• Eu vou enviar o relatório quando a internet voltar a funcionar.

Yes. You can say:

• Quando a internet voltar a funcionar, eu vou enviar o relatório.
• Eu vou enviar o relatório quando a internet voltar a funcionar.

Both mean the same thing.

The first version puts the time condition first, which can feel a little more natural if you want to emphasize when the action will happen.

The second version starts with the main action, which is also very common.

Yes, and in many situations that would sound perfectly natural.

Compare:

• Quando a internet voltar, eu vou enviar o relatório.
• Quando a internet voltar a funcionar, eu vou enviar o relatório.

The second version is a bit more explicit. It clearly says the internet will start working again.

The shorter version, quando a internet voltar, is often understood as when the internet comes back or when the connection is back.

So both are possible; the longer one is just more precise.

Yes. In Brazilian Portuguese, mandar is often used in everyday speech where English would say send.

So you could hear:

• Quando a internet voltar a funcionar, vou mandar o relatório.

Difference in tone:

• enviar = a bit more neutral or formal
• mandar = very common and conversational

Since this sentence is about a relatório, enviar fits especially well in a professional context.

Yes, that can be possible in Brazilian Portuguese, especially in conversation, because the present tense can sometimes refer to a future action.

So:

• eu vou enviar = clearly future, very common
• eu envio = present form with future meaning, possible in context

Still, eu vou enviar is the safest and most obviously future form for learners.

So if you want the most natural, widely usable version, stick with:

• Quando a internet voltar a funcionar, eu vou enviar o relatório.

O relatório is the direct object of enviar.

Structure:

• eu = subject
• vou enviar = verb phrase
• o relatório = direct object

So the sentence is built like this:

• When the internet is working again, I am going to send the report.

Also note:

• relatório is a masculine noun
• that is why it takes o, not a

So:

• o relatório
• not a relatório