De ontvanger controleerde het adres en de postcode voordat zij de brief opende.

Dutch nouns have grammatical gender, and that determines whether they take de or het in the singular.

• de ontvanger = a de-word
• het adres = a het-word

Unfortunately, this is something you usually have to learn with each noun. There are some patterns, but many nouns are simply memorized with their article.

In this sentence:

• de ontvanger = the recipient
• het adres = the address
• de postcode = the postal code
• de brief = the letter

A useful habit is to learn nouns as complete units, for example:

• de ontvanger
• het adres
• de postcode
• de brief

Both are in the simple past.

• controleerde comes from controleren
• opende comes from openen

So:

• controleerde = checked
• opende = opened

These are both weak verbs, which means their past tense is formed regularly with -de or -te.

Here the forms are:

• controleren → controleerde
• openen → opende

This sentence is telling a past event in a straightforward narrative way, much like English checked and opened.

Because voordat introduces a subordinate clause, and in Dutch subordinate clauses the conjugated verb usually goes to the end.

So the sentence breaks down like this:

• Main clause: De ontvanger controleerde het adres en de postcode
• Subordinate clause: voordat zij de brief opende

In the subordinate clause, the normal Dutch pattern is:

• conjunction + subject + other elements + verb

So:

• voordat = conjunction
• zij = subject
• de brief = object
• opende = verb at the end

This is one of the most important word-order differences between English and Dutch.

Voordat means before when it introduces a clause.

Here it connects two actions:

• first: checking the address and postcode
• second: opening the letter

So voordat zij de brief opende means before she opened the letter.

This is different from voor, which is usually a preposition meaning things like before, in front of, or for, depending on context.

Compare:

• voor de brief = before/in front of the letter or for the letter depending on context
• voordat zij de brief opende = before she opened the letter

So:

• voor
  • noun phrase
• voordat
  • clause

Zij can mean either:

• she
• they

But here it most naturally means she, because the earlier noun is singular: de ontvanger.

So in this sentence, zij refers back to de ontvanger.

A learner should know, though, that de ontvanger itself is not inherently female. The sentence writer has chosen zij, so the recipient is being treated as female here. If the recipient were male, you would expect hij. If the sentence were rewritten more neutrally, Dutch might use a different strategy.

Also note that Dutch often has both full and reduced pronoun forms:

• zij / ze

Both can mean she, and zij/ze can also mean they depending on context.

Because the two nouns have different articles:

• het adres
• de postcode

Since one is a het-word and the other is a de-word, each noun keeps its own article.

So you must say:

• het adres en de postcode

You cannot use one article for both, because het does not work with postcode, and de does not work with adres.

Even when two nouns are joined by en (and), each noun still needs the correct article.

Because controleren normally takes a direct object in Dutch, just like to check in English.

So:

• De ontvanger controleerde het adres en de postcode
• literally: The recipient checked the address and the postcode

There is no need for a preposition such as naar or van here.

This is similar to English:

• check the address
• not usually check at the address

So the structure is very direct:

• subject: De ontvanger
• verb: controleerde
• object: het adres en de postcode

This is the difference between a main clause and a subordinate clause in Dutch.

In the main clause, Dutch normally follows the verb-second rule:

• De ontvanger controleerde het adres en de postcode

Here, the conjugated verb controleerde is in the second position.

In the subordinate clause introduced by voordat, Dutch changes the word order:

• voordat zij de brief opende

Now the verb opende goes to the end.

So the basic contrast is:

• Main clause: finite verb in second position
• Subordinate clause: finite verb at the end

This is a core Dutch grammar pattern.

Here opende is simply the past tense of openen: opened.

Dutch openen can mean to open, and in many contexts English might say open up, but there is no special extra meaning here. In this sentence it just means the recipient opened the letter.

So:

• de brief openen = to open the letter
• de brief opende = opened the letter

The meaning is straightforward and not especially idiomatic.

In this sentence, de brief is singular because the verb and context point to one specific letter.

• de brief = the letter

If it were plural, you would have:

• de brieven = the letters

Then the clause would be:

• voordat zij de brieven opende

So the singular form here tells you one letter was opened after the address and postcode were checked.

Yes, Dutch could use the perfect tense, but it would sound slightly different in style.

This sentence uses the simple past:

• controleerde
• opende

That is very normal in written narration and storytelling.

A perfect-tense version would be something like:

• De ontvanger heeft het adres en de postcode gecontroleerd voordat zij de brief heeft geopend.

Grammatically possible, but less natural in many narrative contexts. Dutch often prefers the simple past when recounting a sequence of past events in writing.

So the original sentence sounds smooth and natural for describing a past action sequence.