Домофон только что зазвонил, наверное, пришёл курьер.

Домофон usually means an intercom / door-entry system in an apartment building. It is the thing that rings when someone is downstairs at the entrance and wants to be let in.

So here it is not a normal phone. It is specifically the building entrance buzzer/intercom.

Только что is a fixed expression meaning just now, a moment ago, or just in the time sense.

Even though только by itself often means only, in the expression только что you should learn the whole phrase as one unit:

• только = only
• только что = just now

So Домофон только что зазвонил means the intercom rang very recently.

Зазвонил is a perfective verb and often means started ringing or rang as a completed event.

The prefix за- here often marks the beginning of an action:

• звонить = to ring / to be ringing
• зазвонить = to start ringing

In natural English, The intercom just rang is a good translation, even though the Russian verb literally emphasizes the start of the ringing.

If you said домофон звонил, it would sound more like the intercom was ringing or rang repeatedly / for some time, depending on context.

That is the normal marker of the past tense in Russian.

In the past tense, Russian verbs also show gender in the singular:

• зазвонил = masculine
• зазвонила = feminine
• зазвонило = neuter
• зазвонили = plural

Here the subject is домофон, which is a masculine noun, so the verb is зазвонил.

Here наверное means probably and is being used as a parenthetical word, like I suppose / probably / I guess.

That is why it is set off with commas:

• Домофон только что зазвонил, наверное, пришёл курьер.

The commas show that наверное is not a main part of the clause structure; it comments on the speaker’s degree of certainty.

In speech, you would usually hear a slight pause around it.

Here наверное means probably or I guess.

The speaker is making a likely guess based on the intercom ringing:

• the intercom rang
• so it is probably the courier

It is not absolute certainty. It expresses inference.

Пришёл is the past tense of the perfective verb прийти, meaning came / arrived as a completed event.

That fits the situation well: the speaker thinks the courier has arrived.

• пришёл = came / has come / arrived
• приходил = came by / was coming / used to come, depending on context

If you used приходил, it would usually suggest a different meaning, such as someone came by at some point rather than someone has just arrived now.

Russian word order is flexible. Both are possible, but they sound a little different.

Пришёл курьер puts the verb first and the noun after it. This is common when:

• introducing new information
• stating a conclusion
• sounding natural in spoken narration

Here the speaker is reacting to the intercom and making a guess, so наверное, пришёл курьер sounds very natural.

Наверное, курьер пришёл is also possible, but it feels a bit more straightforward and less like an immediate inference.

Because курьер is a masculine noun, and in the past tense the verb agrees with the subject in gender and number.

So:

• пришёл курьер = the courier came
• пришла женщина = the woman came
• пришло письмо = the letter arrived
• пришли гости = the guests came

Russian has no articles, so there is no direct equivalent of English a or the.

Whether курьер means a courier or the courier depends on context.

In this sentence, English might naturally say the courier, because the speaker probably has a specific expected courier in mind. But Russian simply says курьер.

Russian often connects closely related clauses with a comma even when English might prefer a stronger connector.

Here the relationship is something like:

• The intercom just rang, so it’s probably the courier.

Russian leaves that connection implicit:

• Домофон только что зазвонил, наверное, пришёл курьер.

This gives the sentence a natural spoken feel: first the fact, then the conclusion.

Yes. Russian past tense does not match English tense systems one-to-one.

Depending on context, пришёл can correspond to:

• came
• has come
• arrived

In this sentence, English might naturally say either:

• The intercom just rang; it’s probably the courier.
• The intercom just rang; the courier has probably arrived.

So do not expect one Russian past tense form to always equal one specific English tense.

That is very common. In Russian, ё is often written as е in ordinary texts, even though the pronunciation is still ё.

So these are the same word:

• пришёл = with ё written explicitly
• пришел = same word, but ё omitted in writing

For learners, writing ё is helpful because it shows the correct pronunciation and stress more clearly.