لن يستلم المرسل المجهول كلمة المرور أبدا.

لن is a negation word used with the imperfect verb to mean will not in the future.

So:

• لن يستلم = will not receive

This is different from لا, which often negates the present or general/habitual action:

• لا يستلم = does not receive / is not receiving
• لن يستلم = will not receive

In this sentence, لن is the main clue that the action is being denied in the future.

In Arabic, the imperfect verb can cover both present and future meanings, depending on context and particles.

Here, لن forces a future negative meaning:

• يستلم by itself can mean receives / is receiving / will receive
• لن يستلم specifically means will not receive

Also, after لن, the imperfect verb is grammatically in the subjunctive (منصوب). In a fully vowelled version, it would be:

• لَنْ يَسْتَلِمَ

The final vowel changes, but in normal unvowelled writing, you usually do not see that change.

The subject is المرسل المجهول = the unknown sender.

Arabic very often uses verb-first word order, especially in Modern Standard Arabic:

• لن يستلم المرسل المجهول كلمة المرور أبدا
• literally: Will-not-receive the-unknown-sender the-password ever

This is a normal Arabic sentence pattern:

• verb → subject → object

You could also move the subject earlier for emphasis, but the given order is very natural in MSA.

Because المجهول is an adjective describing المرسل, and Arabic adjectives must agree with the noun they describe.

That means the adjective matches the noun in:

• definiteness
• gender
• number
• case

So:

• المرسل = the sender
• المجهول = the unknown

Together:

• المرسل المجهول = the unknown sender

If the noun were indefinite, the adjective would also be indefinite:

• مرسل مجهول = an unknown sender

كلمة المرور is an iḍāfa construction, often called an annexation or noun construct.

It literally looks like:

• كلمة = word
• المرور = passing / access / passage

Together, the phrase means password.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can take الـ
• the whole phrase can still be definite

So:

• كلمة المرور = the password
• not الكلمة المرور

This is one of the most important noun patterns in Arabic.

أبدا adds emphasis and means something like:

• ever
• at all
• in negative sentences, often never

So:

• لن يستلم المرسل المجهول كلمة المرور = The unknown sender will not receive the password
• لن يستلم المرسل المجهول كلمة المرور أبدا = The unknown sender will never receive the password

It strengthens the negation.

A fully vowelled version would be:

لَنْ يَسْتَلِمَ الْمُرْسِلُ الْمَجْهُولُ كَلِمَةَ الْمُرُورِ أَبَدًا

This shows several grammar points clearly:

• يَسْتَلِمَ: subjunctive after لن
• الْمُرْسِلُ: subject, so nominative
• الْمَجْهُولُ: adjective matching the subject
• كَلِمَةَ: direct object, so accusative
• الْمُرُورِ: second term of iḍāfa, so genitive
• أَبَدًا: an adverb in the accusative

Even if you do not usually write the short vowels, they are still there grammatically.

المرسل comes from the verb أرسل = to send.

As a noun, مرسل means:

• sender
• literally, something like one who sends

So in context:

• المرسل المجهول = the unknown sender

This is a very common Arabic pattern: a participle used like a regular noun.

A helpful transliteration is:

lan yastalima al-mursilu al-majhūlu kalimata al-murūri abadan

A few pronunciation notes:

• لن = lan
• يستلم = yastalim(a)
• المرسل = al-mursil
• المجهول = al-majhūl
• كلمة = kalima(ta) in full grammar, though in pause it often sounds more like kalimat
• المرور = al-murūr
• أبدا = abadan

If you pause at the end of the sentence in normal reading, some final short vowels may not be pronounced fully, but the grammatical form is still important to know.

Yes. Both are used.

• كلمة المرور is very common in Modern Standard Arabic, especially in technology and official interfaces.
• كلمة السر is also common and often means password, secret word, or code word.

In many tech contexts, كلمة المرور is the more standard UI-style choice, so it fits this sentence very naturally.