bongtue jusoreul jeokgo uchetonge neoheosseo.

A useful breakdown is:

• 봉투에 = on the envelope / to the envelope
• 주소를 = the address (direct object)
• 적고 = write and / wrote and then
• 우체통에 = into the mailbox / postbox
• 넣었어 = put in (past tense, casual speech)

So the structure is basically:

[place] + [thing written] + write-and + [destination] + put

Korean often puts the main action at the end, so the final verb 넣었어 finishes the whole sentence.

Not exactly, though it is the same particle.

• 봉투에 주소를 적다: here 에 marks the place/surface where something is written, so it feels like on
• 우체통에 넣다: here 에 marks the destination/location something is put into, so it feels like in/into

So 에 is a very flexible location/destination particle. In English we use different prepositions like on, in, and into, but Korean often uses 에 for all of these depending on the verb.

Because 주소 is the thing being written, so it is the direct object of 적다.

• 주소를 적다 = to write the address
• 봉투에 적다 = to write on the envelope

So the sentence has both:

• 봉투에 = where you write
• 주소를 = what you write

This is very common in Korean:

• 종이에 이름을 썼어요 = I wrote my name on the paper
• 벽에 문장을 적었어요 = I wrote a sentence on the wall

-고 connects verbs and usually means and.

So:

• 적고 넣었어 = wrote (it) and put (it) in

In this sentence, it strongly suggests the actions happened in sequence:

1. wrote the address
2. put it in the mailbox

It is one of the most common ways to link actions in Korean.

In Korean, when actions are linked with -고, the tense is often shown only on the final verb.

So:

• 봉투에 주소를 적고 우체통에 넣었어

naturally means that both actions happened in the past, even though only 넣었어 is marked for past tense.

This is very normal Korean. The final verb often carries the tense for the whole sequence.

You can say 적었고 in some situations, but it usually sounds like you are separately emphasizing that first action, rather than just smoothly linking the two actions.

Korean often drops objects that are obvious from context.

Here, the omitted thing is probably:

• the envelope
• the letter
• or it, in a general sense

Since the speaker just mentioned writing the address on the envelope, the listener can easily infer what got put into the mailbox.

If you wanted to say it explicitly, you could say:

• 봉투에 주소를 적고 봉투를 우체통에 넣었어.
• 봉투에 주소를 적고 편지를 우체통에 넣었어.

But in natural Korean, leaving it out is very common.

Because Korean often omits the subject when it is already understood.

So this sentence could mean:

• I wrote the address on the envelope and put it in the mailbox
• He/she wrote the address on the envelope and put it in the mailbox

depending on context.

If you want to include the subject, you can:

• 나는 봉투에 주소를 적고 우체통에 넣었어.

But in everyday Korean, leaving out 나는 is often more natural if the subject is already clear.

넣었어 is:

• past tense
• casual / informal
• commonly used with friends, family, or people you speak comfortably with

Its base form is 넣다 = to put in.

Related forms:

• 넣었어 = casual
• 넣었어요 = polite
• 넣었습니다 = formal

So a polite version of the full sentence would be:

• 봉투에 주소를 적고 우체통에 넣었어요.

Yes, but 적다 is especially natural here.

Both can mean to write, but there is a nuance:

• 쓰다 = to write, in a broad general sense
• 적다 = to write down, jot down, record

For something like an address, name, memo, phone number, or short information, 적다 often sounds very natural.

So:

• 주소를 적다 = very natural
• 주소를 쓰다 = also possible, but slightly less specific in nuance

Usually no. 우체통 means a public postal mailbox/postbox, the kind you drop outgoing mail into.

That is why:

• 우체통에 넣었어

means something like put it in the mailbox/postbox for mailing, not put it in the mailbox at someone’s house.

For English speakers, mailbox can be ambiguous, so postbox is sometimes a clearer translation.

Yes, this word often confuses learners.

넣었어 comes from:

• 넣다
  • -었어

It is commonly pronounced close to 너허써 in careful standard speech.

So even though the spelling looks compact, there is a noticeable ㅎ-type breathy sound in the middle.

This is one reason the word can feel tricky at first: the spelling and the sound are not as transparent as in simpler verbs.