jigwoni upyeonmureul samulhame neoheosseoyo.

A simple breakdown is:

• 직원-이: employee/staff member
  • subject marker -이
• 우편물-을: mail / postal item(s)
  • object marker -을
• 사물함-에: locker
  • location/destination marker -에
• 넣었어요: put in / placed inside in the past polite form

So the sentence structure is:

• subject
  • object
    • place/destination
      • verb

That is a very common Korean pattern.

-이/가 is the subject marker in Korean.

Here, 직원 ends in a consonant, so it takes -이:

• consonant + -이
• vowel + -가

So:

• 직원 → 직원이

It marks 직원 as the subject, the person doing the action.

A learner-friendly way to think of it here is:

• 직원이 = the employee as the one who put something somewhere

-을/를 is the object marker. It marks the thing directly affected by the verb.

Here, the thing being put somewhere is 우편물, so it takes the object marker:

• 우편물 ends in a consonant, so it becomes 우편물을

Pattern:

• consonant + -을
• vowel + -를

So 우편물을 means this noun is the thing that was put into the locker.

Here, -에 marks the destination/location where something is placed.

With verbs like 넣다 (to put in), -에 is very common because it shows the place something goes into or at.

So:

• 사물함에 넣었어요 = put it in/into the locker

This is different from -에서, which usually marks the place where an action happens in a more general sense, like studying at school or eating at a restaurant.

With 넣다, -에 is the natural choice because the locker is the target location.

Because 넣다 focuses on putting something into a destination.

• -에 = to/in/at a destination
• -에서 = at/from the place where an action occurs

In this sentence, the locker is not just the place where the employee happened to be standing. It is the place the mail was put into. That is why 사물함에 fits.

Compare the idea:

• 사물함에 넣다 = put it in the locker
• 사물함에서 would sound like the locker is the place where some action is taking place, which does not fit well with 넣다 here

넣었어요 comes from the dictionary form 넣다, which means to put in.

Formation:

• dictionary form: 넣다
• verb stem: 넣-
• past tense ending: -었-
• polite ending: -어요

So:

• 넣- + 었 + 어요 → 넣었어요

This makes it:

• past tense
• polite
• informal polite style used in everyday conversation

넣었어요 is in the 해요체 style, often called the polite informal style.

It is:

• polite enough for everyday conversation
• common in speech
• less formal than 넣었습니다

Compare:

• 넣었어요 = polite, natural in daily conversation
• 넣었습니다 = more formal, often used in announcements, reports, business situations, or formal writing
• 넣었어 = casual, used with close friends or younger people

Korean nouns often do not have to show singular vs. plural as clearly as English does.

So 우편물 can mean:

• mail
• a piece of mail
• postal items
• mail matter

The exact number is usually understood from context.

That means this sentence could refer to:

• one mail item
• several pieces of mail

Korean often leaves that unspecified unless the speaker wants to make it clear.

사물함 usually means a locker or storage compartment for personal items.

It is made from:

• 사물 = things, belongings, objects
• 함 = box/container/case

So it is literally something like a storage box for belongings.

Important nuance:

• 사물함 is a locker
• it is not automatically a mailbox

So this sentence suggests the mail was put into a locker or storage compartment, not necessarily into a postal mailbox.

Korean is basically an SOV language:

• Subject
• Object
• Verb

So a common order is:

• 직원이 = subject
• 우편물을 = object
• 사물함에 = location/destination
• 넣었어요 = verb

Unlike English, Korean normally puts the verb at the end. That is one of the most important sentence-pattern differences English speakers need to get used to.

Yes. Korean often omits the subject when it is already clear from context.

So in a natural conversation, you might hear:

• 우편물을 사물함에 넣었어요.

This can still be perfectly clear if everyone already knows who did it.

Korean drops information more freely than English when the listener can infer it. That is very normal and natural.

Yes, but the nuance changes.

• 직원이 uses the subject marker and simply identifies the employee as the doer of the action.
• 직원은 uses the topic marker and gives more of a topic/contrast feeling.

For example:

• 직원이 우편물을 사물함에 넣었어요.
  This straightforwardly states that the employee did it.

• 직원은 우편물을 사물함에 넣었어요.
  This can sound more like as for the employee, they put the mail in the locker, possibly contrasting with someone else or continuing a topic already under discussion.

English does not mark this distinction as clearly, so it often feels subtle to learners.

The basic order here is very natural, but Korean word order is more flexible than English because particles show each word’s role.

So these can still be understandable:

• 우편물을 직원이 사물함에 넣었어요.
• 사물함에 직원이 우편물을 넣었어요.

However, the original order is the most neutral and natural in many situations:

• 직원이 우편물을 사물함에 넣었어요.

Changing the order often adds emphasis or changes what sounds most important. For learners, it is best to get comfortable with the neutral pattern first.