jip ap upyeonhame gwanribi annaega deureo isseosseo.

집 앞 is the normal, natural Korean way to say in front of the house.

A few points:

• 앞 means front.
• When a place noun comes before it, Korean often just puts the nouns together:
  • 집 앞 = in front of the house
  • 학교 앞 = in front of the school
  • 문 앞 = in front of the door

Using 집의 앞 is grammatically possible in a very literal sense, but it sounds unnatural in everyday speech. Korean usually avoids 의 in this kind of expression unless it is really needed.

우편함 means mailbox or letter box, and 에 marks the location.

So:

• 우편함에 = in the mailbox

Here, 에 is used because the sentence is describing where something was located. With 있다 and related expressions, 에 often marks the place where something exists or is found.

Compare:

• 책상 위에 책이 있어요. = There is a book on the desk.
• 우편함에 안내가 들어 있었어. = A notice was in the mailbox.

가 marks 관리비 안내 as the subject of the sentence.

So the structure is roughly:

• 집 앞 우편함에 = in the mailbox in front of the house
• 관리비 안내가 = the management-fee notice
• 들어 있었어 = was inside / had been put in there

In Korean, 이/가 often marks the thing that exists, appears, or is located somewhere.

For example:

• 방에 사람이 있어요. = There is a person in the room.
• 우편함에 편지가 들어 있었어. = There was a letter in the mailbox.

관리비 means maintenance fee, building management fee, or apartment fee, depending on context.

안내 means guidance, notice, or information/announcement.

So 관리비 안내 is something like:

• a notice about the maintenance fee
• a management-fee notice
• information regarding the building fee

This kind of noun-noun combination is very common in Korean. The relationship between the nouns is often understood from context.

This is a very common learner question.

• 있었어 just means was there
• 들어 있었어 adds the idea of being inside or having gone in and remained there

So 들어 있다 literally means something like to be in/inside.

Compare:

• 우편함에 안내가 있었어.
  = There was a notice in the mailbox.
  (simple statement of existence)

• 우편함에 안내가 들어 있었어.
  = There was a notice inside the mailbox / A notice had been put in the mailbox.
  (more vivid; emphasizes that it was inserted and sitting inside)

In this sentence, 들어 있었어 sounds very natural because mail or notices are typically put into a mailbox.

It breaks down like this:

• 들어가다 / 들어오다 / 들어오다-related 들어- form in everyday usage often contributes the sense of going/being inside
• 들어 있다 = to be contained in / to be inside
• 들어 있었어 = past form of that expression, so was inside or had been in

In practical learner terms, it is easiest to understand 들어 있다 as a set expression meaning:

• to be inside
• to be contained in
• to be inserted in

Then:

• 들어 있어 = is inside
• 들어 있었어 = was inside

있었어 is in the casual/informal speech style.

Here are the corresponding levels:

• 들어 있었어 = casual, plain speech
• 들어 있었어요 = polite everyday speech
• 들어 있었습니다 = formal speech

So this sentence sounds like something you would say to:

• a friend
• someone younger
• someone you are close to
• in a diary or casual narration

If you wanted to say the same thing politely, you could say:

• 집 앞 우편함에 관리비 안내가 들어 있었어요.

Yes, it helps to read it as one noun phrase:

• 집 앞 = in front of the house
• 우편함 = mailbox

Together:

• 집 앞 우편함 = the mailbox in front of the house

Then with 에:

• 집 앞 우편함에 = in the mailbox in front of the house

Korean often stacks nouns and location expressions before the particle, so it can feel long, but it is built step by step.

No, here 앞 is clearly a location noun, meaning front.

앞 can mean different things depending on context:

• 학교 앞 = in front of the school
• 문 앞 = in front of the door
• 시험 앞두고 = before the exam

In 집 앞 우편함, it is definitely spatial: the mailbox in front of the house.

In some contexts, yes. 안내문 explicitly means notice, written announcement, or posted/written guidance.

So:

• 관리비 안내 = management-fee notice/information
• 관리비 안내문 = written notice about the management fee

Both can be natural, but 안내 is often used broadly in real Korean for notices, guidance, and announcements, especially in everyday context. The version in the sentence sounds natural enough, especially if the speaker is simply referring to the document or notice they found.

Yes, it can.

Because of 들어 있었어, the sentence can suggest not just it existed there, but that it had been placed in the mailbox.

It does not directly say who put it there, but it naturally implies that someone—such as the building office, apartment management, or postal delivery—put the notice into the mailbox.

So the feeling is often a bit closer to:

• There was a management-fee notice in the mailbox
• A management-fee notice had been put in the mailbox

Yes, but the nuance would change.

• 관리비 안내가 들어 있었어
  = A management-fee notice was in there.
  This is a neutral observation or introduction of the item.

• 관리비 안내는 들어 있었어
  = As for the management-fee notice, it was in there.
  This sounds contrastive or topic-marking.

Using 는 might suggest something like:

• the management-fee notice was there, but maybe something else was not
• you are talking specifically about that notice as a known topic

Without a special contrast or topic context, 가 is the more natural default here.

Primarily, it describes a past state: the notice was in the mailbox.

But because of 들어 있다, there is also a faint sense of the earlier action that led to that state—namely, that the notice got put in there.

So the focus is:

• not on the moment it was inserted
• but on the fact that, at that past time, it was sitting inside

That is why English translations can vary a little:

• There was a management-fee notice in the mailbox.
• A management-fee notice had been put in the mailbox.
• A management-fee notice was inside the mailbox.

All of these reflect slightly different angles on the same Korean sentence.