Ako primim odgovor danas, odmah ću ti poslati poruku.

Because primim is the perfective verb form, from primiti = to receive as a completed event.

Croatian often uses:

• primiti = to receive, to get, once/completely
• primati = to be receiving, to receive repeatedly/habitually

In this sentence, the speaker means if I receive the reply today as a single completed event, so primim is the natural choice.

If you used primam, it would sound more like an ongoing or repeated action, which does not fit this situation well.

This is very common in Croatian.

After ako = if, Croatian often uses the present tense of a perfective verb to talk about a future event:

• Ako primim odgovor danas... = If I receive the reply today...

Even though primim looks like present tense, with a perfective verb after ako it refers to a future completed action.

English usually says:

• If I receive...

not

• If I will receive...

So in this respect, Croatian is actually similar to English.

Ću is the clitic form of htjeti used to build the future tense.

Here:

• ću poslati = I will send

So:

• odmah ću ti poslati poruku = I will immediately send you a message

Croatian future tense is commonly formed with:

• ću, ćeš, će, ćemo, ćete, će
  • infinitive

Examples:

• poslat ću = I will send
• ću poslati = I will send

Both patterns exist, though sentence structure affects which one appears more naturally.

In standard Croatian, clitics such as ću usually go in the second position of the clause.

So in:

• odmah ću ti poslati poruku

the clitic ću comes very early in the clause, after the first stressed element.

Also, when the auxiliary comes after the infinitive, the infinitive often loses its final -i:

• poslat ću rather than
• poslati ću

So the most standard options are:

• Odmah ću ti poslati poruku.
• Odmah poslat ću ti poruku. is not natural
• Poslat ću ti poruku odmah. is natural

In your sentence, ću ti poslati is a very normal structure.

Ti here means to you.

It is the dative singular clitic of ti = you in the informal singular.

The verb poslati often takes:

• a direct object: what is sent
• an indirect object in the dative: to whom it is sent

So:

• poslati poruku = to send a message
• poslati ti poruku = to send you a message

Compare:

• tebe = you, as a full/emphatic form, usually not used here
• ti = to you

Because poruku is the accusative singular form of poruka.

• poruka = message
• poruku = message, as the direct object

Since poslati is sending what?

• poruku

So:

• poslati poruku = to send a message

This is a very common feminine noun pattern:

• nominative: poruka
• accusative: poruku

Because odgovor is the direct object of primim, and it is a masculine inanimate noun.

For masculine inanimate nouns, the accusative singular is usually the same as the nominative singular.

So:

• nominative: odgovor
• accusative: odgovor

That is why Croatian says:

• primiti odgovor = to receive a reply

If it were a masculine animate noun, the accusative would usually look different.

Because Croatian usually drops subject pronouns when they are not needed.

The verb endings already show the subject:

• primim = I receive
• ću poslati = I will send

So ja is unnecessary unless you want emphasis or contrast.

For example:

• Ako ja primim odgovor danas... would sound more emphatic, like If I am the one who receives the reply today...

Normally, Croatian prefers simply:

• Ako primim odgovor danas...

Odmah means immediately, right away, or at once.

It is an adverb, and its position is somewhat flexible.

Your sentence has:

• odmah ću ti poslati poruku

That is very natural.

You could also hear:

• Ako primim odgovor danas, ću ti odmah poslati poruku. — less natural because of clitic placement
• Ako primim odgovor danas, poslat ću ti odmah poruku.
• Ako primim odgovor danas, poruku ću ti poslati odmah.

The meaning stays similar, but some versions sound more natural than others. The version in your sentence is a very good standard one.

Because the sentence begins with an ako-clause:

• Ako primim odgovor danas = if I receive the reply today

and then comes the main clause:

• odmah ću ti poslati poruku = I will immediately send you a message

Croatian normally separates this kind of introductory subordinate clause with a comma.

So the comma works much like in English:

• If I receive the reply today, I’ll send you a message immediately.

Yes, Croatian word order is fairly flexible, but not completely free.

For example, these are all possible with small differences in emphasis:

• Ako primim odgovor danas, odmah ću ti poslati poruku.
• Ako danas primim odgovor, odmah ću ti poslati poruku.
• Ako primim danas odgovor, odmah ću ti poslati poruku.
• Ako primim odgovor danas, poslat ću ti odmah poruku.

However, clitics such as ću and ti have placement rules and usually come near the beginning of their clause.

So while many words can move for emphasis, you cannot move everything randomly.

Yes. Poslati is also a perfective verb.

It refers to sending something as a completed act:

• poslati = to send, once/completely
• slati = to send, to be sending, to send repeatedly

In this sentence, the speaker means one completed future action:

• I will send you a message

So poslati is the natural choice.

If you used slati, it would usually suggest a more ongoing or repeated action, which would not match this sentence as well.

Grammatically, danas is inside the if-clause:

• Ako primim odgovor danas = If I receive the reply today

So it directly modifies primim.

The natural interpretation is:

• if the reply arrives today, then I will immediately send you a message

Because of odmah, the second action is understood as happening right after that, likely also today, but danas itself belongs to the first clause.

Yes, you could, but ako is the normal everyday word for if.

• Ako primim odgovor danas... = neutral, common, natural
• Ukoliko primim odgovor danas... = also possible, often a bit more formal or administrative in tone

For everyday speech, ako is the best choice here.