Lähetän hakemuksen sähköpostitse tänään.

Because lähetän is the 1st person singular present tense form of the verb lähettää (to send).

• lähettää = to send
• lähetän = I send / I am sending / I will send

In Finnish, verbs change according to the subject, so you usually do not need to add minä (I) unless you want emphasis.

So:

• Lähetän = I send
• Minä lähetän = I send / I am the one sending (more emphasis)

Finnish often leaves out personal pronouns when the verb ending already shows who is doing the action.

Here, -n in lähetän tells you the subject is I.

So both are possible:

• Lähetän hakemuksen sähköpostitse tänään.
• Minä lähetän hakemuksen sähköpostitse tänään.

The first is more neutral and natural in many situations.

Because it is the object of the verb, and in this sentence Finnish uses the total object form.

• dictionary form: hakemus = application
• here: hakemuksen

This form shows that the speaker is sending the whole application, as a completed item.

A useful contrast:

• Lähetän hakemuksen. = I will send the application / the whole application
• Lähetän hakemusta. = I am sending the application in a more incomplete, ongoing, or partial sense

In many beginner explanations, hakemuksen is described as looking like the genitive form, and that is true in form. In this sentence, it functions as the total object.

Sähköpostitse means by email, via email, or through email.

It tells you the means or method used to send the application.

So:

• Lähetän hakemuksen sähköpostitse. = I send / will send the application by email

This word is built from sähköposti (email) plus a form that expresses by way of / via.

Yes. Both can mean by email.

• sähköpostitse = by email, via email
• sähköpostilla = by email, with email

Both are understandable and common, though they can sound slightly different in style depending on context.

Very roughly:

• sähköpostitse can sound a bit more formal or fixed-expression-like
• sähköpostilla can sound a bit more everyday

So this sentence could also be:

• Lähetän hakemuksen sähköpostilla tänään.

But sähköpostitse is perfectly natural.

It can mean all of those, depending on context.

Finnish present tense often covers:

• I send
• I am sending
• I will send

In this sentence, because of tänään (today), English will often translate it as:

• I’ll send the application by email today.

So even though Finnish uses the present tense form, the meaning can be future.

Finnish word order is fairly flexible. The word tänään (today) can appear in different places depending on what you want to emphasize.

These are all possible:

• Lähetän hakemuksen sähköpostitse tänään.
• Tänään lähetän hakemuksen sähköpostitse.
• Lähetän tänään hakemuksen sähköpostitse.

The basic meaning stays similar, but the emphasis changes a little.

For example:

• Tänään first can emphasize today
• keeping it at the end can sound neutral and natural

Yes. It is a very natural sentence.

A simple way to look at it is:

• Lähetän = verb
• hakemuksen = object
• sähköpostitse = method
• tänään = time

Finnish does not rely on word order as strictly as English does, because endings carry a lot of grammatical information. That means Finnish can move parts around more freely for emphasis.

Still, the sentence as given is completely normal.

It is one word: sähköpostitse.

Finnish often forms adverb-like expressions as a single word. So unlike English, where you say by email as two words, Finnish can use one combined form.

Because tänään is a common Finnish adverb meaning today.

It does not change form here, and it answers the question when?

• Milloin? = When?
• Tänään. = Today.

So in the sentence, it tells you when the action happens.

Possibly, but in most contexts it more naturally suggests that the sending happens at some point today, not necessarily right this second.

If you wanted to strongly emphasize right now, Finnish would usually add something like:

• nyt = now
• parhaillaan = currently

For example:

• Lähetän hakemuksen sähköpostitse nyt. = I am sending the application by email now.
• Lähetän hakemusta parhaillaan. = I am in the process of sending the application.

So the original sentence is broader: today is the important time frame.

A helpful breakdown is:

• Lähetän = I send / I will send
• hakemuksen = the application
• sähköpostitse = by email
• tänään = today

So the structure is roughly:

verb + object + method + time

That makes the sentence easy to understand as:

I will send the application by email today.