Learn Hardcore Japanese: watasi ha takuhaibin de nimotu wo okurimasu.

In a neutral statement like this, introducing yourself as the topic with 私は is very common. Using が (私が宅配便で荷物を送ります) would put special emphasis on I (and not someone else) am the one who will send it, often in a contrastive or corrective way:

私が送ります。 = I’ll send it (not him / not you / not someone else).

So:

私は荷物を送ります。 = plain, neutral “I send / I will send the package.”
私が荷物を送ります。 = emphasizes I as the one doing it.

Do I actually need to say 私 here? Japanese people often drop pronouns, right?

You do not need 私 in most real conversations if it’s already clear who is sending the package.

Natural everyday version:
宅配便で荷物を送ります。

Because the speaker is usually obvious from context, Japanese often omits 私, あなた, etc. You would keep 私は if:

You are introducing new information about yourself (e.g., self-introduction).
You want to contrast yourself with others:
みんなはメールで送りますが、私は宅配便で荷物を送ります。
Everyone else sends it by email, but I send the package by courier.

In simple, context-rich situations, 宅配便で荷物を送ります on its own is the most natural.

What exactly does the particle で mean in 宅配便で?

Here で marks the means / method used to perform the action.

宅配便で = “by courier service,” “via courier,” “using a delivery service.”

This is the same で you see in:

バスで行きます。 – I go by bus.
メールで送ります。 – I send it by email.

So the basic pattern is:

[method / tool] + で + [action]
宅配便で + 送ります = send it by courier.

Could I say 宅配便に荷物を送ります instead of 宅配便で?

No, 宅配便に荷物を送ります is not natural for this meaning.

に often marks a destination / target (e.g., 友だちに手紙を送る – send a letter to a friend).
宅配便 is not the destination; it is the means.

Because 宅配便 is the method, not the recipient, Japanese uses で:

宅配便で荷物を送ります。 – I will send the package by courier.

If you want to mark the recipient, you would use に or へ for that person:

友だちに宅配便で荷物を送ります。
I will send a package by courier to my friend.

What is the role of を in 荷物を送ります?

を marks the direct object of the verb – the thing that undergoes the action.

荷物を送ります。
荷物 (package) is what is being sent, so it takes を.

Very common pattern:

本を読みます。 – read a book.
水を飲みます。 – drink water.
メールを送ります。 – send an email.

In casual speech, people sometimes drop を when it’s obvious:

荷物送ります。 (spoken casual)

But in writing or in careful/learner Japanese, it’s better to keep を.

Is the word order fixed? Can I say 荷物を宅配便で送ります instead?

Yes, you can. Both are natural:

宅配便で荷物を送ります。
荷物を宅配便で送ります。

Japanese word order is:

[various phrases] + verb at the end

The parts before the verb are relatively flexible. The nuance:

Putting 宅配便で first slightly highlights the method:
宅配便で荷物を送ります。 – As for how, I’ll send the package by courier.
Putting 荷物を first puts a bit more focus on the package:
荷物を宅配便で送ります。 – As for the package, I’ll send it by courier.

Both are perfectly fine; the difference is very subtle in most contexts.

What level of politeness is 送ります, and how is it different from 送る?

送ります is the polite form (the ます form).
送る is the plain / dictionary form.

送ります – used in most conversations with people who are not very close, at work, in stores, etc.
送る – used with family, good friends, in casual online chat, in dictionaries, and inside complex grammar patterns.

Examples:

Polite: 明日、宅配便で荷物を送ります。
Plain: 明日、宅配便で荷物を送る。

Meaning is the same; only the speech level changes. As a learner, using 送ります is a safe default in most situations.

The verb is in the “present” tense (送ります). How can it mean “I will send” (future)?

Japanese basically has two main tense forms:

Non-past: 送る / 送ります – covers present and future.
Past: 送った / 送りました – covers past.

So:

送ります。 can mean
- I send (generally / habitually), or
- I will send (in the future).

Which one it is depends on context:

Talking about a plan:
明日、宅配便で荷物を送ります。 – I will send the package tomorrow.
Talking about a routine:
いつも宅配便で荷物を送ります。 – I always send packages by courier.

There is no separate future tense form like English “will send.”

What’s the difference between 送る and other verbs like 届ける or 出す for packages?

All relate to sending/delivering, but the nuance differs:

送る – to send something from you to someone else (focus on the act of sending).
- 宅配便で荷物を送ります。 – I’ll send the package by courier.
届ける – to deliver / bring something so that it reaches the destination (focus on arrival/delivery).
- 荷物を家に届けます。 – I’ll deliver the package to the house.
出す – to put out / submit / mail / send out (focus on “sending out” or “handing in”).
- 荷物を郵便局から出します。 – I’ll send out the package from the post office.
- 手紙を出します。 – I’ll mail a letter.

For your original sentence, 送る is the most natural general verb for “send a package by courier.”

What does 宅配便 specifically mean? Is it just “mail,” or something more specific?

宅配便 literally combines:

宅 – home
配 – deliver
便 – service

It refers to a door-to-door parcel delivery service, like a courier company that picks up or delivers packages to your home or office.

Often contrasted with 郵便 (postal mail, post office services).
In everyday Japanese, 宅配便 suggests services like Yamato, Sagawa, etc.

So:

宅配便で荷物を送ります。 – I’ll send the package by courier / parcel delivery service, not just by regular letter mail.