Estou prestes a enviar o texto ao professor, a não ser que você queira ler primeiro.

Estar prestes a + infinitive means to be about to + verb.

So:

• Estou prestes a enviar = I’m about to send

It shows that the action is going to happen very soon, almost immediately.

A few examples:

• Estou prestes a sair. = I’m about to leave.
• Ela está prestes a começar. = She’s about to start.

It is a very natural expression in Portuguese.

Both can work, but they are not exactly the same.

• Estou prestes a enviar = I’m just about to send it; the action feels very imminent.
• Vou enviar = I’m going to send it; this is more general and does not necessarily mean right now.

So estou prestes a enviar adds a stronger sense of I’m on the verge of doing it.

Because prestes a is the fixed pattern used before an infinitive.

Structure:

• estar prestes a + infinitive

Examples:

• estou prestes a dormir
• estamos prestes a começar
• ele está prestes a cair

You should learn prestes a as a chunk.

Ao is a contraction of:

• a
  • o = ao

Here, o professor is masculine singular, so the contraction is ao professor.

So:

• enviar o texto ao professor = send the text to the professor

Other related forms:

• a + a = à
• a + os = aos
• a + as = às

For example:

• Entreguei o livro ao aluno.
• Escrevi à professora.

Yes, in many everyday situations para o professor would also sound natural.

So both are possible:

• enviar o texto ao professor
• enviar o texto para o professor

Very broadly:

• a / ao can sound a bit more tied to the verb’s indirect object structure
• para often feels more conversational and clearly directional

In modern Brazilian Portuguese, para o professor is extremely common in speech. But ao professor is also completely natural and often sounds a bit more formal or polished.

A não ser que means unless.

It introduces an exception:

• Estou prestes a enviar o texto ao professor, a não ser que você queira ler primeiro.
• I’m about to send the text to the professor, unless you want to read it first.

Think of it as: except if / unless.

It is a set expression, so it’s best to learn it as a whole.

Because a não ser que normally requires the subjunctive.

So after a não ser que, Portuguese uses the present subjunctive:

• a não ser que você queira = unless you want

Not:

• a não ser que você quer ❌

This is one of the common cases where Portuguese uses the subjunctive because the clause expresses something uncertain, conditional, or dependent on a possibility.

Queira is the present subjunctive form of querer for:

• eu
• você
• ele/ela
• o senhor / a senhora

In this sentence, it matches você:

• você queira

Present subjunctive of querer:

• que eu queira
• que você queira
• que ele/ela queira
• que nós queiramos
• que vocês queiram
• que eles/elas queiram

Because in Brazilian Portuguese, você takes third-person singular verb forms.

So:

• você quer
• você queira
• você vai
• você leu

Even though você means you, grammatically it behaves like he/she for verb conjugation.

This is completely normal in Brazilian Portuguese.

Primeiro here means first, and placing it after the infinitive is very natural:

• ler primeiro = read first

This word order is common and sounds smooth in Brazilian Portuguese.

You may also hear:

• primeiro ler

but in this sentence ler primeiro is the more natural choice.

So:

• você queira ler primeiro = you want to read it first

Because it is understood from the previous part of the sentence.

The full idea is:

• ler o texto primeiro

But once o texto has already been mentioned, Portuguese can leave it out if the meaning is obvious:

• você queira ler primeiro

English does the same:

• I’m about to send the text to the professor, unless you want to read it first.

Portuguese often omits that repeated object when context makes it clear.

The comma is very natural here because the sentence has:

• a main clause: Estou prestes a enviar o texto ao professor
• followed by an exception clause: a não ser que você queira ler primeiro

The comma helps separate the two parts clearly. In writing, this is the normal and best choice.