När boken finns i lager igen, skickar de ett mejl till mig.

När means when and is used when the speaker sees the situation as something expected to happen. Here, the idea is that the book will be back in stock at some point.

Om means if and would make it sound more uncertain or conditional.

• När boken finns i lager igen ... = When the book is back in stock ...
• Om boken finns i lager igen ... = If the book is back in stock ...

So när is the natural choice here.

This is because Swedish follows the V2 rule in main clauses: the finite verb must come in the second position.

The first position here is the whole opening clause:

När boken finns i lager igen

After that, the main clause begins, and the finite verb skickar must come before the subject de:

• När boken finns i lager igen, skickar de ett mejl till mig.

If the sentence started directly with the subject, then you would say:

• De skickar ett mejl till mig.

Swedish very often uses the present tense for future meaning when the context already makes the future clear.

Here, när ... igen already tells you this is about a future situation, so Swedish does not need a separate future form.

This is very common:

• Jag kommer i morgon. = I’m coming tomorrow.
• Vi ses nästa vecka. = We’ll see each other next week.

So finns and skickar are present tense in form, but future in meaning.

Boken is the definite form, meaning the book. It shows that we are talking about a specific book already known from the context.

• en bok = a book
• boken = the book

The definite ending is added to the noun itself in Swedish:

• bok → boken

So this sentence is about a particular book, not just any book.

Finns is the present tense of finnas, which often means to exist, to be available, or to be found.

In this sentence, it means something like is available or is in stock.

So boken finns i lager is a natural Swedish way to say that the book is available in stock.

You may hear similar expressions, but finns i lager is very natural when talking about whether something is available for purchase.

Swedish often uses finnas for availability:

• Varan finns i lager. = The item is in stock / available.

So for learners, finns i lager is a very useful and idiomatic pattern to remember.

I lager means in stock or in inventory.

It is a common expression used for products in shops, warehouses, and online stores.

You may also see på lager in Swedish. Both are used, but in this sentence i lager is completely natural.

Igen means again, and here it belongs with the idea be in stock again.

In Swedish, adverbs like igen often come after the rest of the verb phrase or expression:

• kommer hem igen = comes home again
• blir frisk igen = gets well again
• finns i lager igen = is in stock again

So the placement is normal and natural.

Here de means they, but it does not have to mean a specific named group. It can refer generally to the people responsible, such as:

• the store
• the company
• the website staff

English does this too: They’ll email me when it’s back in stock.

So de is being used in a general, practical way.

Because mejl is an ett-word in Swedish.

That means:

• ett mejl = an email
• mejlet = the email

Swedish nouns belong to either en or ett gender, and you simply have to learn which one each noun takes.

Swedish often uses skicka något till någon = send something to someone.

So:

• skickar de ett mejl till mig = they send an email to me

You can also say:

• skickar de mig ett mejl

That is also correct. The version with till mig can feel a bit clearer or more explicit, especially for learners.

Not strictly. In modern Swedish, a comma after an opening subordinate clause is often optional.

So both of these are possible:

• När boken finns i lager igen skickar de ett mejl till mig.
• När boken finns i lager igen, skickar de ett mejl till mig.

The comma can help readability, especially in longer sentences, but it is not always required.

In everyday spoken Swedish, de is very often pronounced dom.

So although it is written de, you will usually hear something close to dom in normal speech.

This is one of the most common pronunciation surprises for learners.