Hun bruker c/o-adressen dersom navnet hennes ikke står på postkassen.

Hun is the standard Bokmål subject pronoun for she.

• Hun = she
• Henne = her

You may also see ho in Nynorsk and in some dialects, but hun is the normal Bokmål form here.

Bruker is the present tense of å bruke (to use).

So:

• å bruke = to use
• bruker = uses / is using
• brukte = used
• har brukt = has used

In this sentence, Norwegian uses the present tense to state a general fact or habit:

• Hun bruker c/o-adressen ... = She uses the c/o address ...

This sounds like something she does whenever the condition applies.

c/o stands for care of, just like in English postal addresses.

Adressen means the address, and c/o-adressen means the c/o address or the care-of address.

The -en ending is the definite article attached to the noun:

• en adresse = an address
• adressen = the address

So c/o-adressen is a compound noun:

• c/o + adressen

The hyphen is used because c/o is an abbreviation/symbol-like element joined to a noun.

In Norwegian, compounds are often written as one word, but when the first part is an abbreviation, symbol, letter, or something visually awkward, a hyphen is often used for clarity.

So:

• c/o-adressen is the natural written form

Dersom means if.

Yes, it is very close in meaning to hvis. In many contexts, they are interchangeable.

• dersom = if
• hvis = if

Dersom can sound a little more formal or careful than hvis, but both are common and correct.

So this sentence could also be written as:

• Hun bruker c/o-adressen hvis navnet hennes ikke står på postkassen.

Both are possible in Norwegian, but they are used a little differently.

The most common neutral pattern is:

• navnet hennes = her name

This is the typical Norwegian way: noun + possessive.

You can also say:

• hennes navn

But that structure is often more emphatic, more formal, or used for contrast.

So in ordinary everyday Norwegian, navnet hennes sounds the most natural here.

Because hennes refers specifically to her and avoids ambiguity.

Norwegian often uses reflexive possessives such as:

• sin / sitt / sine

These are used when the possessor is the subject of the clause.

However, in this sentence the phrase navnet hennes is inside the subordinate clause dersom navnet hennes ikke står på postkassen. Using sitt here would sound odd because navnet is not something that possesses itself, and sin/sitt/sine must clearly refer back to the subject in the same clause.

The natural expression is:

• navnet hennes = her name

That is the normal and idiomatic choice here.

In Norwegian, stå is often used where English would say be written, be listed, or appear.

So:

• navnet står på postkassen literally = the name stands on the mailbox
• natural English meaning = the name is on the mailbox / the name is written on the mailbox

This is a very common Norwegian use of stå.

Similar examples:

• Det står i avisen. = It says so in the newspaper.
• Navnet mitt står på døra. = My name is on the door.

Because the meaning is on the mailbox, not in the mailbox.

• på = on
• i = in

Here the sentence is talking about a name written or displayed on the outside of the mailbox, so på is correct:

• navnet hennes ikke står på postkassen = her name is not on the mailbox

If you said i postkassen, that would mean in the mailbox, which is a different idea.

Because in Norwegian, ikke usually comes before the finite verb in a subordinate clause.

The clause here is introduced by dersom, so it is a subordinate clause:

• dersom navnet hennes ikke står på postkassen

Compare:

Main clause:

• Navnet hennes står ikke på postkassen.

Subordinate clause:

• ... dersom navnet hennes ikke står på postkassen.

This is a very important word order rule in Norwegian.

Yes, it is definite because it means the mailbox.

• en postkasse = a mailbox
• postkassen = the mailbox

In Norwegian, the definite article is usually attached to the noun as an ending:

• -en for many common gender nouns
• -et for neuter nouns
• -a / -en for feminine/common patterns depending on style

Here:

• postkasse → postkassen

Yes. The structure is very natural:

• Hun = subject
• bruker = verb
• c/o-adressen = object
• dersom ... = subordinate clause giving the condition

So the pattern is:

• [Main clause] + [subordinate clause]

Inside the subordinate clause, the word order is also normal:

• navnet hennes = subject phrase
• ikke = negation
• står = verb
• på postkassen = prepositional phrase

This is standard Norwegian syntax.

Yes. You could say:

• Dersom navnet hennes ikke står på postkassen, bruker hun c/o-adressen.

That means the same thing.

Notice what happens in the main clause after the subordinate clause comes first:

• bruker hun
• not hun bruker

This is because Norwegian keeps the finite verb in the second position in main clauses. So when the sentence starts with the subordinate clause, the verb comes before the subject in the main clause.

It most naturally expresses a general rule, habit, or usual situation.

• Hun bruker c/o-adressen dersom ... = She uses the c/o address if/whenever ...

Because the sentence is in the present tense, it sounds like a regular practice rather than one single event.

If you wanted a past situation, you would normally change the tense:

• Hun brukte c/o-adressen dersom navnet hennes ikke sto på postkassen.
  or more naturally depending on context:
• Hun brukte c/o-adressen hvis navnet hennes ikke sto på postkassen.