Eu não consegui abrir o arquivo, mas minha prima conseguiu mandar o e-mail.

Because the subject changes.

• Eu não consegui = I didn’t manage / I wasn’t able
• minha prima conseguiu = my cousin managed / was able

Both forms come from the verb conseguir.

In the pretérito perfeito (simple past), the forms are:

• eu consegui
• você/ele/ela conseguiu

So:

• consegui = I managed
• conseguiu = he/she/you managed

The ending changes to match the subject.

Because after conseguir, Portuguese normally uses another verb in the infinitive.

So the structure is:

• conseguir + infinitive

Examples:

• Consegui abrir o arquivo. = I managed to open the file.
• Ela conseguiu mandar o e-mail. = She managed to send the email.

This is similar to English manage to + verb, except Portuguese does not need a separate word like to before the second verb.

In Portuguese, não usually goes directly before the verb it negates.

So:

• Eu não consegui = I didn’t manage
• Ela não abriu = She didn’t open

This is the normal position for negation in straightforward sentences.

Yes. Portuguese often drops subject pronouns when the verb form already makes the subject clear.

So these are both natural:

• Eu não consegui abrir o arquivo...
• Não consegui abrir o arquivo...

Because consegui clearly shows eu, the pronoun is not required.

However, keeping Eu can add:

• emphasis
• contrast
• clarity

In this sentence, Eu can help set up the contrast with minha prima:

• Eu não consegui..., mas minha prima conseguiu...

Because Portuguese uses definite articles very often, often more than English does.

• o arquivo = the file
• o e-mail = the email

If the speaker has a specific file and a specific email in mind, the definite article is natural.

Portuguese frequently uses articles with nouns where English might sometimes leave them out.

Both are possible in Brazilian Portuguese.

• minha prima
• a minha prima

Both can mean my cousin.

In Brazilian Portuguese, possessives like meu/minha/seu/sua may appear:

• with an article
• without an article

The version without the article is very common and sounds perfectly natural here.

Yes.

• prima = female cousin
• primo = male cousin

So minha prima can only refer to a female cousin.

Mas means but and introduces contrast.

Here the contrast is:

• I couldn’t open the file,
• but my cousin could send the email.

So mas connects two ideas that go in different directions.

Because mas is a coordinating conjunction, and in Portuguese it is normally preceded by a comma when it links two full clauses.

So this punctuation is standard:

• Eu não consegui abrir o arquivo, mas minha prima conseguiu mandar o e-mail.

This is similar to English punctuation with but in many cases.

They are two different verb + object combinations:

• abrir o arquivo = to open the file
• mandar o e-mail = to send the email

A useful point is that arquivo in Portuguese often means a computer file, not just an archive in English.

So in this sentence:

• arquivo is very likely a digital file
• e-mail is the email message

Both are possible.

• mandar um e-mail
• enviar um e-mail

In Brazilian Portuguese, mandar is very common in everyday speech and often sounds a bit more informal and conversational.

• mandar = send
• enviar = send

In this sentence, mandar o e-mail sounds natural and idiomatic.

In this sentence, conseguir is closest to manage to or be able to in the past.

• não consegui abrir o arquivo = I didn’t manage to open the file
• minha prima conseguiu mandar o e-mail = my cousin managed to send the email

It often suggests whether the action was successfully completed, not just general ability.

So conseguir is often more result-focused than simply could.

Yes. In Brazilian Portuguese, both e-mail and email are seen.

• e-mail is very common
• email is also widely accepted

The noun is usually masculine:

• o e-mail
• o email

So the sentence could also appear as:

• ...mandar o email.

Normally, no. In this sentence, repeating the verb is the natural way to say it.

• Eu não consegui abrir o arquivo, mas minha prima conseguiu mandar o e-mail.

If you remove conseguiu, the sentence becomes ungrammatical or unclear.

Portuguese often repeats the verb when the subject changes and each clause needs its own predicate.

It is in the simple past, called the pretérito perfeito in Portuguese.

• consegui
• conseguiu

These forms describe completed actions in the past.

So the sentence talks about a finished situation:

• I didn’t manage to open the file
• my cousin did manage to send the email

It is not the imperfect (conseguia), which would suggest an ongoing or habitual past situation.