Jag känner inte avsändaren, så jag öppnar inte mejlet.

In Swedish, känna is used for knowing a person or being familiar with someone/something.

• Jag känner avsändaren = I know the sender
• Jag vet is used for knowing a fact
  • Jag vet vem avsändaren är = I know who the sender is

So in this sentence, känner is the natural choice because the speaker means they do not know the sender as a person or identity.

No. Känna can mean several related things, depending on context:

• to know a person: Jag känner henne
• to feel physically or emotionally: Jag känner mig trött
• to sense / notice in some expressions

So känner is a flexible verb. In this sentence, it means know.

In a normal Swedish main clause, the negative word inte usually comes after the finite verb.

Pattern:

• subject + verb + inte + rest

So:

• Jag känner inte avsändaren
• Jag öppnar inte mejlet

This is one of the most important word-order patterns in Swedish.

Because Swedish usually adds the to the end of the noun instead of using a separate word before it.

• avsändare = sender

• avsändaren = the sender

• mejl = email
• mejlet = the email

This is called the definite form of the noun.

Avsändare is a common-gender noun (en word), so its definite singular form usually ends in -en.

• indefinite: en avsändare = a sender
• definite: avsändaren = the sender

So the -en ending is what makes it definite.

Because mejl is usually treated as a neuter noun in Swedish, an ett word.

• ett mejl = an email
• mejlet = the email

For many ett words, the definite singular ending is -et.

Compare:

• ett hus → huset
• ett brev → brevet
• ett mejl → mejlet

Here, så means so or therefore.

It connects the two clauses:

• Jag känner inte avsändaren = I don't know the sender
• så jag öppnar inte mejlet = so I don't open the email

It shows cause and result.

Because in this sentence så is being used as a coordinating conjunction, similar to and, but, or so in English.

After a coordinating conjunction, Swedish normally keeps normal main-clause word order:

• ..., så jag öppnar inte mejlet

There is no inversion here.

The base forms (infinitives) are:

• känna → känner
• öppna → öppnar

The sentence uses the present tense.

So:

• jag känner = I know / I am knowing
• jag öppnar = I open / I am opening

In Swedish, the present tense does not change for different persons:

• jag känner
• du känner
• han/hon känner

Because Swedish main clauses follow the verb-second pattern. In a simple subject-first sentence, that gives you:

• Jag öppnar inte mejlet

The finite verb (öppnar) must come early in the clause, and inte comes after it.

Jag inte öppnar mejlet sounds wrong as a normal main clause.

Sometimes, yes, but mejl and mejlet are very common in modern Swedish.

You may see different spellings:

• mejl / mejlet
• mail / mailet in some informal contexts
• e-post for a more formal or traditional word

For learners, mejl is a good standard everyday choice.

It is singular definite:

• ett mejl = an email
• mejlet = the email

Plural would be:

• mejl = emails
• mejlen = the emails

So this sentence is talking about one specific email.

That would mean something slightly different.

• Jag känner inte avsändaren = I don't know the sender
• Jag känner inte igen avsändaren = I don't recognize the sender

So känner inte igen is about recognition, not general familiarity. Depending on context, either could make sense, but they are not the same.

Because avsändaren is more specific. It means the sender, especially the sender of a message, email, letter, etc.

• personen = the person
• avsändaren = the sender

In an email context, avsändaren is the precise word Swedish would often use.

It is neutral, natural everyday Swedish.

• Jag känner inte avsändaren sounds a bit careful or clear
• jag öppnar inte mejlet is very normal everyday language

So the whole sentence sounds perfectly natural in standard Swedish, neither especially formal nor especially slangy.