Ο θυρωρός ανοίγει το γραμματοκιβώτιο μόνο όταν υπάρχει πρόβλημα με τα κλειδιά.

Θυρωρός usually means doorman, porter, or building caretaker.

In this kind of sentence, it often refers to the person in charge of an apartment building entrance, mail, keys, and small practical issues. So it is not just any guard; it has a building-related sense.

Ο is the definite article meaning the.

Here, ο θυρωρός means the doorman and it also shows that the noun is:

• masculine
• singular
• nominative case

The nominative is used because ο θυρωρός is the subject of the sentence: he is the one doing the action.

Greek often leaves out subject pronouns when they are not needed.

The verb ανοίγει already tells you the subject is third person singular: he/she/it opens.

So Greek does not need to say he unless the speaker wants extra emphasis or contrast.

For example:

• Ο θυρωρός ανοίγει... = The doorman opens...
• Αυτός ανοίγει... would add emphasis, something like he is the one who opens...

Ανοίγει is the present tense of ανοίγω.

In Greek, the present tense can mean:

• a habitual action: opens
• an action happening right now: is opening

In this sentence, because of μόνο όταν and the general meaning, it is understood as a habitual or general action:

• The doorman opens the mailbox only when there is a problem with the keys.

So this is not about one specific moment, but about what usually happens.

Το γραμματοκιβώτιο means the mailbox.

A few useful points:

• γραμματοκιβώτιο is a neuter noun
• το is the neuter singular article
• it is the direct object of ανοίγει

For many neuter nouns in Greek, the nominative and accusative forms are the same. So you see:

• το γραμματοκιβώτιο as subject
• το γραμματοκιβώτιο as object

Same form, different job in the sentence.

Also, the word is built from:

• γράμμα = letter
• κιβώτιο = box

So it is literally something like letter-box.

Μόνο όταν means only when.

• μόνο = only
• όταν = when

Together they introduce a condition or restricted circumstance:

• μόνο όταν υπάρχει πρόβλημα = only when there is a problem

So the idea is that the doorman does not open the mailbox in general, but only in that specific situation.

Υπάρχει means there is / there exists.

Greek often uses υπάρχει to express existence, just like English uses there is.

So:

• υπάρχει πρόβλημα = there is a problem

This is different from έχει, which usually means has.

So Greek says:

• υπάρχει πρόβλημα = there is a problem

not:

• έχει πρόβλημα in this sentence

Although έχει πρόβλημα can mean he/she/it has a problem, that is a different structure.

In υπάρχει πρόβλημα, the noun appears without an article because it is indefinite and introduces something new:

• there is a problem

This is very natural in Greek.

You could also hear:

• υπάρχει ένα πρόβλημα = there is a problem / there is one problem

Adding ένα makes the indefiniteness more explicit. But the version without it is very common and natural.

So:

• υπάρχει πρόβλημα = neutral, natural
• υπάρχει ένα πρόβλημα = also possible, sometimes slightly more specific or emphatic

Με means with, and in Modern Greek it is followed by the accusative.

So:

• με τα κλειδιά = with the keys

Here, τα κλειδιά is:

• neuter plural
• accusative
• from the singular το κλειδί = the key

In this sentence, με τα κλειδιά means something like:

• with the keys
• involving the keys
• related to the keys

So πρόβλημα με τα κλειδιά is a very natural way to say a problem with the keys.

Greek word order is more flexible than English word order.

The sentence as given is a very natural, neutral version:

• Ο θυρωρός ανοίγει το γραμματοκιβώτιο μόνο όταν υπάρχει πρόβλημα με τα κλειδιά.

But Greek could also say:

• Μόνο όταν υπάρχει πρόβλημα με τα κλειδιά, ο θυρωρός ανοίγει το γραμματοκιβώτιο.

That version puts more focus on the condition only when there is a problem with the keys.

So the word order can change, but the original sentence is perfectly standard and natural.

A rough pronunciation guide for an English speaker:

• ο θυρωρός ≈ o thee-ro-ROS
• ανοίγει ≈ a-NI-yi
• το γραμματοκιβώτιο ≈ to gra-ma-to-ki-VO-ti-o
• μόνο όταν ≈ MO-no O-tan
• υπάρχει ≈ i-PAR-hi
• πρόβλημα ≈ PRO-vli-ma
• με τα κλειδιά ≈ me ta kli-DYA

A few sounds to notice:

• θ sounds like th in thin
• χ sounds like a rough h/k sound, not exactly an English sound
• γι in ανοίγει sounds like a y sound
• ει is pronounced like ee

The stressed syllable is marked by the accent, so:

• θυρωρός
• ανοίγει
• γραμματοκιβώτιο
• υπάρχει
• πρόβλημα
• κλειδιά