A kaució is az e-mailben van.

Both a and az mean the.

Hungarian has two forms of the definite article:

• a before a consonant sound
• az before a vowel sound

So:

• a kaució = the deposit
• az e-mailben = in the email

Even though English always uses the, Hungarian switches between a and az for pronunciation reasons.

Because e-mail begins with a vowel sound, Hungarian uses az before it.

This is similar to how English uses a / an:

• a book
• an email

Hungarian does the same kind of sound-based adjustment:

• a könyv
• az e-mail

So az e-mailben is the natural form.

is usually means also or too.

In A kaució is az e-mailben van, the is is attached to kaució, so it means something like:

• the deposit too
• the deposit is also in the email

This suggests that something else was already mentioned, and now the speaker is adding the deposit to that list.

A key point: is usually comes right after the word it emphasizes.

So:

• A kaució is... = the deposit too / the deposit also...

In Hungarian, is is normally placed directly after the word or phrase it belongs to.

So:

• A kaució is... = the deposit too
• Az e-mailben is... = in the email too

Those do not mean the same thing.

In your sentence, the speaker is emphasizing that the deposit is also included. If you moved is, the emphasis would change.

-ban / -ben is a Hungarian case ending meaning in.

So:

• e-mailben = in the email

Hungarian often uses endings instead of separate prepositions.

Compare:

• English: in the email
• Hungarian: az e-mail-ben

The suffix has two forms:

• -ban
• -ben

This is because of vowel harmony.

Because Hungarian uses vowel harmony.

Very roughly:

• words with back vowels usually take -ban
• words with front vowels usually take -ben

In e-mail, the pronounced vowels are treated as front-vowel-type in Hungarian usage, so:

• e-mailben

For a learner, the important thing is simply to memorize this form as e-mailben.

That is a very common question.

Hungarian often omits van (is) in the 3rd person singular when the sentence links a subject to a noun or adjective:

• A ház nagy. = The house is big.
• Ő tanár. = He/She is a teacher.

But when the sentence expresses location or existence, van is normally used:

• A könyv az asztalon van. = The book is on the table.
• A kaució az e-mailben van. = The deposit is in the email.

So here van is needed because the sentence says where something is.

That is a normal Hungarian word order in a neutral statement about location.

Structure:

• A kaució is = topic / what we are talking about
• az e-mailben = location
• van = is

So van often comes near the end in sentences like this.

Hungarian word order is flexible, but it is not random. Changing the order usually changes the emphasis.

No, kaució is a loanword, and it means deposit in contexts like renting.

It behaves like a normal Hungarian noun, though, so you can use it with articles and suffixes just like other nouns:

• a kaució
• a kauciót
• a kaucióban (if context allowed)

So even though it is borrowed, grammatically it works like an ordinary Hungarian noun.

Not naturally in standard Hungarian, at least not in this context.

With a specific noun like kaució, you normally use the article if you mean the deposit:

• A kaució...

And with e-mailben, if you mean in the email (a specific one), you also use the article:

• az e-mailben

So A kaució is az e-mailben van is the natural standard version.

If you wanted in an email, you would normally say:

• egy e-mailben

Yes, a little.

A kaució is az e-mailben van sounds like the speaker is adding information:

• something else is in the email,
• and the deposit is too.

Because is follows kaució, the emphasis is on the deposit being an additional item.

If you changed the position of is, the meaning focus would shift:

• A kaució az e-mailben is van.
  = The deposit is also in the email
  (perhaps it is somewhere else too)

So the current sentence highlights kaució as the thing being added.

In Hungarian, e-mail is typically pronounced close to émél or ímél, depending on usage and speaker, and e-mailben is pronounced accordingly with the -ben ending added.

For a learner, the most important practical point is:

• it is treated as a single unit,
• and then the Hungarian ending is attached:
  • e-mail + ben = e-mailben

This kind of mixing of a borrowed word with a Hungarian suffix is very common.

A simple breakdown is:

• A kaució = the deposit
• is = also / too
• az e-mailben = in the email
• van = is

So the pattern is:

[subject] + is + [location] + van

That makes it a straightforward Hungarian location sentence, with is adding the meaning also/too.