Tallennan kuitin verkkopankista ja lähetän sen sähköpostiosoitteeseen, jonka pomo antoi.

Because Finnish often leaves the subject pronoun out when the verb ending already shows who the subject is.

• Tallennan = I save / I store
• Lähetän = I send

The ending -n tells you the subject is I. So minä is usually unnecessary unless you want emphasis or contrast.

• Tallennan kuitin = I save the receipt
• Minä tallennan kuitin = I save the receipt (with extra emphasis)

The dictionary forms are tallentaa and lähettää.

Kuitin is the object form here.

In this sentence, the receipt is treated as a complete thing being saved, so Finnish uses a total object. With a singular noun in this kind of sentence, that often looks like the genitive form:

• kuitti = receipt
• kuitin = the receipt, as a complete object

So:

• Tallennan kuitin = I save the receipt

If you used kuittia, that would suggest something more incomplete, ongoing, or indefinite, which would not fit as well here.

Verkkopankista comes from verkkopankki, meaning online bank / online banking service.

The ending -sta means out of / from.

So:

• verkkopankki = online bank
• verkkopankista = from the online bank

In this sentence, it means the receipt is being saved from the online banking service.

Sen refers back to kuitin: it means it.

Here too, the pronoun is the object of the verb lähetän, so Finnish uses the object form:

• se = it
• sen = it, as the object

So:

• lähetän sen = I send it

This sen does not mean possession here. It is just the correct object form.

Sähköpostiosoitteeseen is the illative form of sähköpostiosoite.

• sähköposti = email
• osoite = address
• sähköpostiosoite = email address
• sähköpostiosoitteeseen = into/to the email address

The illative case often expresses movement or direction into or to something. With lähettää, this is natural for an address:

• lähetän sen sähköpostiosoitteeseen = I send it to the email address

If you were sending something to a person instead, Finnish often uses -lle:

• lähetän sen pomolle = I send it to the boss

But for an address, osoitteeseen is the normal choice.

Because the relative pronoun must match its role inside the relative clause, not the form of the noun it refers to in the main clause.

The relative clause is:

• jonka pomo antoi = which the boss gave

Inside that clause, the email address is the thing that was given, so it is the object of antoi. That is why Finnish uses jonka.

A useful comparison:

• joka = who/which, subject form
• jonka = whose / which, object-or-genitive form
• johon = into which / to which

Here it is not johon, because inside pomo antoi ..., the address is not a destination; it is the thing given.

Not necessarily.

It means the email address that the boss gave/provided. In other words, the boss gave the address to someone, and that is the address being used.

So the idea is:

• the boss provided an email address
• I send the receipt to that address

If you specifically wanted to say the boss’s email address, you would more naturally say:

• pomon sähköpostiosoitteeseen = to the boss’s email address

So these are different:

• sähköpostiosoitteeseen, jonka pomo antoi = to the email address that the boss gave
• pomon sähköpostiosoitteeseen = to the boss’s email address

Finnish often leaves that kind of information out if it is already clear from context or not important.

So:

• jonka pomo antoi = that the boss gave
• jonka pomo antoi minulle = that the boss gave me

Both are possible. The shorter version is very natural if the listener can easily understand who received the address.

Because Finnish normally separates a relative clause with a comma.

Here the relative clause is:

• jonka pomo antoi

It describes sähköpostiosoitteeseen, so a comma is used before it.

This is more regular in Finnish than in English: Finnish commonly uses a comma before relative clauses like this.

Finnish word order is fairly flexible, but the original order is natural and neutral.

• Tallennan kuitin verkkopankista ja lähetän sen... sounds straightforward and neutral.

You can move parts around for emphasis, but that changes the focus:

• Verkkopankista tallennan kuitin... emphasizes from the online bank
• Sen lähetän sähköpostiosoitteeseen... emphasizes it

So yes, the order can change, but not randomly. The usual order here is a good basic model for learners.