Наш почтальон всегда говорит «Здравствуйте», когда кладёт письма в почтовый ящик.

Because почтальон is a masculine singular noun, so the possessive adjective must agree with it in gender, number, and case. The subject here is nominative singular, so the correct form is наш.

• masculine: наш
• feminine: наша
• neuter: наше
• plural: наши

So наш почтальон = our postman / our mail carrier.

It is in the nominative case because it is the subject of the sentence: the mail carrier is the person doing the actions.

So in Наш почтальон всегда говорит..., почтальон is the one who говорит and кладёт.

Russian often uses the present tense for habitual actions, just like English does in sentences such as He always says hello.

The word всегда means always, so the sentence describes something that happens regularly, not just once. That is why говорит is present tense: it means says or is in the habit of saying.

Here it means says.

The verb говорить can mean both to speak and to say, depending on context. When it is followed by reported words or a quoted expression like Здравствуйте, it usually means to say.

So:

• говорит по-русски = speaks Russian
• говорит: Здравствуйте / говорит Здравствуйте = says Hello / Good day

Because it is the exact word the person says. Russian often puts directly quoted words or short set expressions in quotation marks.

So говорит «Здравствуйте» means says “Hello” / “Good day”.

Using quotation marks makes it clear that this is the actual greeting, not just a general description of speaking.

Здравствуйте is a formal or polite greeting. It is what you would say to someone you do not know well, to an older person, or in a respectful situation.

It is more formal than Привет.

So this sentence suggests that the mail carrier is being polite and respectful.

Because Russian often omits subject pronouns when the subject is already clear from context.

In English, you usually need to repeat the pronoun:
Our mail carrier always says hello when he puts letters into the mailbox.

In Russian, once наш почтальон has already been introduced, it is natural to leave out он in the second clause:

Наш почтальон всегда говорит «Здравствуйте», когда кладёт письма...

The verb form кладёт already shows that the subject is he / she / it.

Literally, когда means when, but in a sentence with a habitual meaning like this one, it is often understood as whenever.

So here the sense is:

Our mail carrier always says hello whenever he puts letters into the mailbox.

This is a very common use of когда in Russian.

Кладёт is the 3rd person singular form of the verb класть, meaning to put / to place.

• infinitive: класть
• he/she puts: кладёт

The letter ё shows the stressed sound yo. In many everyday Russian texts, ё is often written as е, so you may also see кладет, but it is still pronounced кладёт.

For learners, it is useful to remember the form with ё, because it helps with pronunciation and stress.

Because письма is the plural form of письмо.

• singular: письмо = letter
• plural: письма = letters

It is the direct object of кладёт, so it is in the accusative plural. Since письмо is an inanimate noun, its accusative plural looks the same as its nominative plural: письма.

Because after в, Russian uses different cases depending on meaning:

• в + accusative = motion into something
• в + prepositional = location in something

Here the letters are being put into the mailbox, so Russian uses the accusative:

• в почтовый ящик = into the mailbox

If you were talking about where something already is, you would use the prepositional:

• в почтовом ящике = in the mailbox

Почтовый is an adjective meaning postal or mail-. It agrees with ящик in gender, number, and case.

Since ящик is masculine singular accusative, and it is inanimate, the accusative form looks the same as the nominative:

• nominative: почтовый ящик
• accusative: почтовый ящик

So nothing visibly changes here, but the adjective is still agreeing grammatically with the noun.

Because когда кладёт письма в почтовый ящик is a subordinate clause.

In Russian, subordinate clauses are normally separated by a comma. The comma here marks the beginning of the when clause.

So:

Наш почтальон всегда говорит «Здравствуйте», когда кладёт письма в почтовый ящик.

This is standard Russian punctuation.

Yes. Russian word order is more flexible than English word order, although the original sentence sounds natural and neutral.

For example, you could also say:

Когда кладёт письма в почтовый ящик, наш почтальон всегда говорит «Здравствуйте».

This still means the same thing, but the emphasis changes slightly. Putting the когда clause first gives more focus to the situation or timing.

The original version is probably the most straightforward and neutral for a learner.

Yes, that is possible, but the meaning is a little less explicit.

• говорит «Здравствуйте» = literally says “Hello”
• здоровается = greets people / says hello

So a sentence like Наш почтальон всегда здоровается... would sound natural too. The version with говорит «Здравствуйте» is simply more concrete, because it tells you the exact word he says.