Неизвестный получатель указан в приложении.

Because неизвестный is agreeing with получатель.

• получатель is masculine
• it is singular
• it is in the nominative case here

So the adjective also has to be masculine singular nominative, which gives неизвестный.

This phrase неизвестный получатель means unknown recipient.

Because it is the grammatical subject of the sentence.

The basic structure is:

• Неизвестный получатель = the unknown recipient
• указан = is indicated / is specified
• в приложении = in the attachment / appendix / enclosure

So получатель is the thing being described as specified somewhere, which makes it the subject.

Указан is the short passive participle of указать, and in this sentence it works like is indicated or is specified.

A few important points:

• указан = short form passive participle, masculine singular
• it describes the state/result: has been indicated
• in Russian, short passive participles are very common in formal or written language

Compare:

• получатель указан = the recipient is specified
• получатель указывается = the recipient is being specified / is specified in a more process-like or general sense

Also, указаный is incorrect spelling. The correct long-form participle would be указанный, with -нн-.

In the present tense, Russian usually does not use a separate word for is / am / are.

So:

• Неизвестный получатель указан в приложении literally looks like Unknown recipient indicated in attachment
• but the natural English meaning is The unknown recipient is indicated in the attachment

This is completely normal in Russian.

В приложении literally means in the attachment, in the enclosure, or sometimes in the appendix.

Which translation fits best depends on context:

• in an email: in the attachment
• in a document or book: in the appendix
• in a formal letter with extra papers: in the enclosure

A learner should be careful because приложение can also mean app/application in modern Russian, especially in tech contexts. But in this sentence, в приложении most likely means in the attached file/document or in the appendix, not in the app.

Because it is the prepositional singular form of приложение after the preposition в.

Dictionary form:

• приложение

After в meaning in, we usually use the prepositional case:

• в приложении

This noun is neuter, and many neuter nouns in -ие change like this:

• nominative: приложение
• prepositional: в приложении

Compare:

• в здании
• в сообщении
• в задании

Russian has no articles, so the sentence itself does not directly mark a vs the.

So неизвестный получатель could be understood as:

• an unknown recipient
• the unknown recipient

The correct English choice depends on context.

For example:

• in a system message, Unknown recipient specified in the attachment
• in a translation with fuller English style, The unknown recipient is indicated in the attachment

Russian leaves that distinction to context.

Yes. Russian word order is more flexible than English, although the neutral order here is very natural.

Current order:

• Неизвестный получатель указан в приложении.

Possible alternatives:

• В приложении указан неизвестный получатель.
• Указан неизвестный получатель в приложении. (less neutral)

The meaning stays similar, but the emphasis changes.

For example:

• В приложении указан неизвестный получатель emphasizes where the recipient is indicated
• Неизвестный получатель указан в приложении is a straightforward neutral statement

Yes, especially in formal, administrative, or technical contexts. It sounds like something you might see in:

• an error message
• a document-processing system
• official correspondence
• software interface text

It is a bit formal and compact. In everyday conversation, a speaker might use a fuller or less formal phrasing depending on the situation.

Both can relate to the person who receives something, but they are not always identical.

• получатель = recipient, receiver
• адресат = addressee, the person to whom something is addressed

In many contexts they overlap, especially with messages, mail, or documents. But:

• получатель often focuses on receiving
• адресат often focuses on being addressed to

In this sentence, получатель is perfectly natural if the context is delivery, transfer, message routing, or a form that identifies who receives something.

Its core meaning is unknown, but depending on context it can sometimes feel like:

• not identified
• unspecified
• not recognized
• unfamiliar

In a sentence like this, the most likely meaning is that the recipient is not identified or not known to the system / reader.

So here unknown recipient is the best interpretation.