nimotu ga buzi ni todoita to sitte, hottosita.

荷物が marks 荷物 as the subject of 届いた: the package is the thing that arrived.

Using は would be possible in some contexts, but it would make 荷物 more of a topic, as in as for the package.... In this sentence, the focus is simply on the fact that the package arrived safely, so が sounds natural.

• 荷物が届いた = The package arrived
• 荷物は届いた = As for the package, it arrived / The package did arrive

無事に means safely, without problems, or without incident.

So 荷物が無事に届いた means the package arrived and nothing went wrong with it. This is very common with deliveries, travel, and people arriving somewhere safely.

Examples:

• 無事に着いた = arrived safely
• 無事に終わった = ended without problems

Here, 無事に works adverbially: it modifies the verb 届いた and tells you how the package arrived.

So:

• 無事に届いた = arrived safely

You may also see 無事で in other structures, but in this sentence 無事に + verb is the normal pattern.

Because 届く and 届ける are different verbs:

• 届く = to arrive (intransitive)
• 届ける = to deliver (transitive)

In this sentence, the package is the thing that arrived, so 届く is correct:

• 荷物が届いた = The package arrived

If you used 届けた, there would need to be someone delivering something:

• 彼が荷物を届けた = He delivered the package

This と marks the content of what was learned or known. It works a bit like that in English.

• 荷物が無事に届いたと知って
  = knowing that the package arrived safely

So the whole clause before と is the information that became known.

This is a very common pattern:

• 〜と聞く = hear that ...
• 〜と思う = think that ...
• 〜と言う = say that ...
• 〜と知る = learn/know that ...

The て-form connects this part to what follows.

• 荷物が無事に届いたと知って、ほっとした。 = I learned that the package arrived safely, and I felt relieved. = Knowing that the package arrived safely, I felt relieved.

Here the て-form shows that the first event leads into the second. It often has a sense like:

• when
• after
• because

So the sentence implies: After I found out, I felt relieved.

In this sentence, it is closer to finding out or learning than simply already knowing.

That is because ほっとした happens as a reaction to the new information. So the feeling of relief comes when the speaker learns the package arrived safely.

A natural English translation would be:

• When I learned that the package had arrived safely, I felt relieved.

ほっとする means to feel relieved or to feel a weight come off your mind.

It comes from ほっと, an expression that suggests a small breath of relief, like whew.

So:

• ほっとした = felt relieved
• ほっとする = to feel relieved

This expression is very common in everyday Japanese.

Examples:

• 試験が終わってほっとした。 = I felt relieved when the exam was over.
• 無事だと聞いてほっとした。 = I was relieved to hear that they were safe.

The subject is omitted, which is very common in Japanese. It is usually understood from context.

Here, the person who learned the news and felt relieved is most naturally:

• I or possibly
• we

So the sentence is understood as something like:

• I felt relieved when I learned that the package had arrived safely.

Japanese often leaves out subjects when they are obvious.

Because the clause before と is the content being known: the package arrived safely.

Japanese uses plain forms before particles like と in this kind of embedded clause.

So:

• 届いた = arrived
• 届いたと知って = learned that it arrived

This is normal even if the whole sentence is polite or informal.

For example:

• informal: 届いたと知って、ほっとした。
• polite: 届いたと知って、ほっとしました。

The verb before と stays plain.

Yes, 荷物が無事に届いたことを知って is possible, but と知って is very natural and direct here.

Very roughly:

• 〜と知って often feels like learning or realizing a piece of information
• 〜ことを知って can sound a little more nominalized, treating the whole clause as a fact

In many cases both are grammatical, but と知って is a very common choice with this kind of sentence.

Yes, but the nuance changes slightly.

• 荷物が無事に届いたと知って、ほっとした。

  • smooth narrative connection
  • when I learned that ..., I felt relieved

• 荷物が無事に届いたと知ったら、ほっとした。

  • more like when/once I found out
  • can sound a bit more conditional or event-based

The original sentence with 知って is very natural for describing the emotional sequence.

A simple polite version is:

荷物が無事に届いたと知って、ほっとしました。

Only the final verb becomes polite here. That is very common.

You could also say: 荷物が無事に届いたと知り、ほっとしました。

This sounds a bit more written or formal than 知って.