Learn Hardcore Japanese: tomodati kara meeru wo morau to uresii desu. - I am happy when I receive an email from a friend.

So here から is like English “from”.
(Other common uses of から exist, like “because” or “from (a point in time)”, but here it’s clearly “from (a person)”.)

Why is it 友達から and not 友達に?

With もらう (to receive), both 〜から and 〜に can mark the giver, but から is more common and natural when talking about receiving something from someone.

友達からメールをもらう – very natural
友達にメールをもらう – grammatically possible, but less common in everyday speech

If you switch the verb to あげる (to give), then に is what you normally use:

友達にメールをあげる – to give/send an email to a friend

What does メールをもらう literally mean?

Literally:

メール – “mail”, in modern usage usually “email”
を – object marker
もらう – “to receive (for oneself)”

So メールをもらう = to receive an email.

The receiver (here, “I”) is usually omitted in Japanese because it’s obvious from context.
The full idea in natural English is: “When I receive an email from a friend…”

Why is the subject “I” not written in the sentence?

Japanese often omits the subject if it’s clear from context.

In this sentence, who would be happy when they get an email from a friend? Naturally, it’s the speaker (or sometimes “you”, depending on context). So Japanese leaves it out:

(私は) 友達からメールをもらうと嬉しいです。
(I) am happy when I receive an email from a friend.

Leaving out 私は (I) is completely normal and usually sounds more natural.

What does the と after もらう do here?

This と is a conditional that can be translated as “when” or “whenever”.

Pattern: Verb (dictionary form) + と + result

It’s often used for:

regular, habitual situations
natural or automatic results

So:

友達からメールをもらうと嬉しいです。
= When / Whenever I get an email from a friend, I feel happy.

This isn’t “quoting と”, but the conditional と.

Could we say 友達からメールをもらったら嬉しいです instead? What’s the difference?

Yes, you can say that, and it’s correct:

友達からメールをもらったら嬉しいです。
If I get an email from a friend, I’ll be happy.

Nuance:

〜と〜 often implies a general, habitual or automatic result.
“When that happens, that always follows.”
〜たら〜 (past form + ら) is a more general “if/when”, often used for one-time or more hypothetical situations.

In your original sentence with と, it sounds like a regular fact about you:
> Whenever I get an email from a friend, I feel happy.

With たら, it can sound more situational / one-off:
> If I get an email from a friend (this time), I’ll be happy.

Why is it 嬉しいです and not just 嬉しい?

嬉しい is an い-adjective meaning “happy, glad.”

嬉しい – plain/casual
嬉しいです – polite

Adding です makes the whole sentence polite, which matches the rest of the sentence. In conversation:

Casual: 友達からメールをもらうと嬉しい。
Polite: 友達からメールをもらうと嬉しいです。

Both are correct; the choice depends on politeness level.

Is the verb もらう in present tense or future tense here?

Japanese doesn’t clearly separate present and future tenses the way English does. The dictionary form (もらう) can cover:

present (habitual): I get
future: I will get

With と in this pattern, it usually expresses a general, habitual situation:

友達からメールをもらうと嬉しいです。
= I’m happy when I get emails from friends.
(implying “whenever that happens, I feel happy”)

So it’s more about habit/regularity than a specific future event.

Why is the word order 友達からメールをもらう and not “メールを友達からもらう”?

Both orders are grammatically correct:

友達からメールをもらう
メールを友達からもらう

Japanese word order is fairly flexible as long as the particles are correct. The most important rule is that the verb comes at the end. Everything else can usually move around.

The original order 友達からメールをもらう is very natural and flows well, but メールを友達からもらう would also be understood without any problem.

What kind of word is 嬉しい? Is it a verb or an adjective?

嬉しい is an い-adjective (形容詞).

Characteristics of い-adjectives:

They end in 〜い in dictionary form.
They can directly modify nouns:
- 嬉しいニュース – happy news
They conjugate like verbs in some ways:
- 嬉しくない – not happy
- 嬉しかった – was happy
- 嬉しくなかった – was not happy

It’s not a verb; it’s an adjective meaning “happy/glad.”

Why is there no particle after 友達? Shouldn’t there be something like 友達は?

The particle is actually there: 友達から.

友達 – friend
から – from

So 友達から together means “from (a) friend.”
You could also add a topic marker elsewhere (for example 私は at the beginning), but it’s optional:

私は友達からメールをもらうと嬉しいです。
(As for me,) I’m happy when I get an email from a friend.

In the original, the topic and subject are just omitted because they’re obvious from context.

Is 友達 always singular “friend,” or can it mean “friends” too?

友達 by itself does not mark singular or plural; context decides.

It can mean a friend
Or friends (in general)

In English you’d choose based on what sounds natural:

友達からメールをもらうと嬉しいです。
→ “I’m happy when I get an email from a friend.”
or
→ “I’m happy when I get emails from friends.”

Both are valid translations; Japanese doesn’t force you to choose singular/plural here.