Na terça-feira à noite, eu vou responder ao e-mail da empresa.

Na is the contraction of em + a. With days of the week, Brazilian Portuguese very often uses no/na to mean on:

• na terça-feira = on Tuesday
• na quarta-feira = on Wednesday

You can sometimes hear just the weekday by itself in certain contexts, but na terça-feira is a very natural, standard way to say on Tuesday.

The names of weekdays from Monday to Friday are written with -feira and a hyphen:

• segunda-feira
• terça-feira
• quarta-feira
• quinta-feira
• sexta-feira

This is just the standard spelling in Portuguese. Saturday and Sunday are different: sábado and domingo.

À noite means at night or in the evening/night, depending on context.

The à has a grave accent because it is a contraction of two a's:

• the preposition a
• the feminine article a

This kind of contraction is called crase.

So:

• à noite = at night / in the evening
• a noite without the accent would usually mean the night as a noun, not the time expression

That is just how these common time expressions work in Portuguese:

• de manhã = in the morning
• à tarde = in the afternoon
• à noite = at night / in the evening

So the pattern is not fully identical for all parts of the day. This is something learners usually just memorize as fixed expressions.

Yes, you can hear de noite in Brazilian Portuguese, especially in casual speech. But à noite is very common and often feels a bit more neutral or standard in this kind of sentence.

So:

• na terça-feira à noite = very natural
• na terça-feira de noite = also possible in many contexts

Yes, vou already shows that the subject is I, so the sentence could simply be:

Na terça-feira à noite, vou responder ao e-mail da empresa.

Portuguese often drops subject pronouns when the verb form is clear. Adding eu is still completely correct. It can make the sentence feel a little clearer, more explicit, or slightly more emphatic.

Vou responder is the near future construction:

• vou = I go / I am going
• responder = to answer / to reply

Together, vou responder means I am going to answer or I will answer.

This structure, ir + infinitive, is extremely common in Brazilian Portuguese for talking about the future.

A more formal or less conversational alternative would be:

• responderei = I will answer

But in everyday speech, vou responder is much more common.

The verb responder commonly takes the preposition a when it means to answer or to reply to someone or something.

So:

• responder a algo
• responder a alguém

Since e-mail is masculine and takes o, the combination becomes:

• a + o = ao

So:

• responder ao e-mail = reply to the email

You may also hear some Brazilians say responder o e-mail in informal speech, but responder ao e-mail is the more standard form.

Da is the contraction of de + a:

• de = of / from
• a = the

So da empresa means of the company or from the company, depending on context.

In this sentence, o e-mail da empresa could mean:

• the company’s email
• the email from the company

The exact meaning comes from context.

Both e-mail and email are seen in Brazilian Portuguese. E-mail has been very common for a long time, but email is also widely used now.

So learners should recognize both:

• o e-mail
• o email

In your sentence, e-mail is perfectly fine.

Yes. Portuguese allows some flexibility here. For example, you could also say:

Eu vou responder ao e-mail da empresa na terça-feira à noite.

This means the same thing. Starting with Na terça-feira à noite simply puts the time first, which is very natural if you want to set the scene first.

The comma after the introductory time expression is also normal and helpful.

It can mean either Tuesday evening or Tuesday night, depending on the situation. Portuguese noite often covers both what English separates into evening and night.

So na terça-feira à noite is a natural translation for:

• on Tuesday evening
• on Tuesday night

Context tells you which one is more natural in English.