atesaki wo matigaetara, sasidasinin no tokoro ni nimotu ga modotte kurukoto ga arimasu.

宛先（あてさき） means the destination / addressee / address you are sending something to.

In a shipping context, it often refers to the recipient information written on a package. So in English, it may be translated as address, but more literally it is the person/place it is addressed to.

The を marks 宛先 as the thing being mistaken.

So 宛先を間違える means to get the address wrong or to make a mistake in the destination/addressee.

This is a very common pattern:

• 名前を間違える = to get the name wrong
• 番号を間違える = to get the number wrong
• 道を間違える = to take the wrong road / get the route wrong

間違えたら is the past short form of 間違える plus ら, making a conditional.

So:

• 間違える = to make a mistake
• 間違えた = made a mistake
• 間違えたら = if you make / made a mistake

In English, this often translates naturally as if you get the address wrong.

The たら conditional is very common for if/when situations.

Japanese often leaves the subject unstated when it is obvious or unimportant.

Here, the sentence does not explicitly say you, someone, or the sender. The meaning is more general:

If the address is written incorrectly / if someone gets the address wrong, the package may be returned to the sender.

That kind of omitted subject is extremely normal in Japanese.

差出人（さしだしにん） means sender.

差出人のところに literally means to the sender’s place.

Here, ところ does not just mean a physical spot in a strict sense. It often means the person’s side / the person’s place / where that person is. In this sentence, it naturally means:

back to the sender

So:

• 差出人に would also suggest to the sender
• 差出人のところに adds the nuance of to the sender’s end / back to where the sender is

Because 荷物 is the thing that comes back, so it is the subject of 戻ってくる.

• 荷物が戻ってくる = the package comes back
• が marks the subject

You would not use を with 戻ってくる here, because the package is not a direct object; it is the thing performing the action of returning.

戻る means to return / go back.

戻ってくる adds the idea of coming back toward a reference point.

In this sentence, the reference point is the sender’s side:

• 荷物が戻る = the package returns
• 荷物が戻ってくる = the package comes back

In English, comes back often sounds more natural here, because the package is returning to the sender.

ことがあります means there are times when..., it may happen that..., or sometimes....

So:

• 荷物が戻ってくることがあります = the package may come back
• or sometimes the package comes back

This expression is often used to describe:

• possible occurrences
• things that happen from time to time
• a non-absolute statement

It makes the sentence less direct than saying it always happens.

Because こと is treated as a thing/event, not a person or animal.

In Japanese:

• あります is used for things, events, abstract matters
• います is used for people and animals

Here, 戻ってくること means the event/fact of coming back, so あります is correct.

Yes, basically.

差出人のところ literally means the sender’s place or the sender’s side.

The particle の links 差出人 and ところ, showing that the ところ belongs to or is associated with the sender.

This pattern is very common:

• 先生のところ = the teacher’s place / the teacher
• 友だちのところ = a friend’s place / to the friend
• 会社のところ = the company’s side

Sometimes, but the nuance is different.

• 宛先 = destination / recipient address / where it is being sent
• 宛名 = the name of the recipient written on the mail/package

So:

• if the whole destination information is wrong, 宛先 fits well
• if the recipient’s name itself is wrong, 宛名 may be more appropriate

In this sentence, 宛先 is a natural choice because it refers broadly to the shipping destination information.

It is neutral to fairly formal and very natural in written instructions, postal explanations, customer service notices, or general guidance.

Features that make it sound a bit formal/informational:

• vocabulary like 宛先 and 差出人
• the structure ことがあります
• the absence of personal wording like あなたが

It sounds like the kind of sentence you might see on a mailing guide or shipping website.