Он не только не ответил на мой запрос, но и не открыл письмо.

This is a very common Russian correlative structure meaning not only ..., but also ....

In your sentence:

• не только не ответил на мой запрос
• но и не открыл письмо

So the speaker is listing two negative actions:

1. he did not reply to the request
2. he did not open the letter

Russian often uses:

• не только X, но и Y = not only X, but also Y

Here both parts are negative, so each verb keeps its own не.

The first не belongs to the expression не только = not only.

The second не belongs to the verb:

• не ответил = did not reply

So these are doing two different jobs:

• не только = a linking expression
• не ответил = the actual negation of the verb

That is why не только не ответил is correct.

Compare:

• Он не только опоздал, но и забыл документы.
  = He not only arrived late, but also forgot the documents.

• Он не только не позвонил, но и не пришёл.
  = He not only didn’t call, but also didn’t come.

In this pattern, Russian normally uses the full pair:

• не только ..., но и ...

The и reinforces the idea of also / as well.

So:

• но = but
• но и = but also

Without и, the sentence may sound incomplete or less standard in this structure. The full pairing is what learners should remember.

Because the verb ответить often takes the preposition на when you are replying to something such as:

• ответить на вопрос = answer a question
• ответить на письмо = reply to a letter
• ответить на запрос = reply to a request/inquiry

So Russian does not say this the same way English does. English says reply to a request, but Russian says literally answer onto/for a request using на.

This is just a verb pattern you need to learn:

• ответить кому? = reply to someone
• ответить на что? = reply to something

Examples:

• Я ответил ему. = I replied to him.
• Я ответил на его письмо. = I replied to his letter.

Because на here requires the accusative case, and запрос is:

• masculine
• inanimate

For masculine inanimate nouns, the accusative form is the same as the nominative:

• запрос → запрос

And the matching possessive adjective is also the same in this case:

• мой запрос

So:

• nominative: мой запрос
• accusative: мой запрос

That is why the form does not visibly change.

If it were a feminine noun, you would usually see a clearer change:

• на мою просьбу = to my request/plea

Because the sentence talks about completed, one-time actions that did not happen.

• ответил is perfective from ответить
• открыл is perfective from открыть

The meaning is not about process or repeated behavior. It is about the result:

• he did not reply
• he did not open

Perfective is very natural here because the speaker is evaluating whether these actions were completed.

Compare:

• Он не ответил. = He did not reply.
  Focus: no completed reply happened.

• Он не отвечал. = He was not replying / He did not reply over a period / He never replied in that context.
  Focus: process, duration, or repeated/non-occurring action.

Similarly:

• не открыл письмо = did not open the letter
• не открывал письмо = did not open the letter at any point / was not opening it

In this sentence, perfective is the most natural choice.

It could, but the meaning would shift.

• не ответил and не открыл sound like clear facts about completed actions that failed to happen.
• не отвечал and не открывал would sound more descriptive, process-based, or situational.

For example:

• Он не только не отвечал на мой запрос, но и не открывал письмо.

This can sound like:

• he wasn’t responding
• he wasn’t opening the letter
• over some period of time

That is possible in context, but it is not quite the same as the original sentence, which presents two definite failures as completed facts.

Russian often leaves out repeated subjects when they are obvious.

So in:

• Он не только не ответил на мой запрос, но и не открыл письмо

the subject он naturally applies to both verbs:

• he did not reply
• and he did not open

You could repeat он, but usually it would sound unnecessary unless you wanted extra emphasis or contrast.

Natural version:

• Он не только не ответил на мой запрос, но и не открыл письмо.

More emphatic or contrastive:

• Он не только не ответил на мой запрос, но и он не открыл письмо.

The second is much less neutral.

Because the sentence has two coordinated parts linked by the correlative construction не только ..., но и ....

Russian punctuation normally puts a comma before the second part:

• Он не только не ответил на мой запрос, но и не открыл письмо.

This is similar to how English often separates the two halves of not only ..., but also ....

These words are related, but they are not the same.

• запрос = request, inquiry, formal request, query
  Often used in business, official, technical, or customer-service contexts.

• просьба = request in the sense of asking someone to do something; often more personal
  Example: У меня к тебе просьба.

• вопрос = question
  Example: ответить на вопрос = answer a question

So ответил на мой запрос suggests something like:

• a formal request
• an inquiry
• a submitted query
• maybe even a support or business request

That is why запрос fits well in a formal or professional context.

It can mean either, depending on context.

Traditionally:

• письмо = letter

But in modern usage it is also very commonly used for:

• an email

So не открыл письмо could mean:

• he didn’t open the letter
• he didn’t open the email

If the broader context is digital communication, many speakers will understand it as email automatically.

Yes. The structure не только ..., но и ... adds emphasis.

Compare:

• Он не ответил на мой запрос и не открыл письмо.
  = He didn’t reply to my request and didn’t open the letter.

• Он не только не ответил на мой запрос, но и не открыл письмо.
  = He not only didn’t reply to my request, but also didn’t open the letter.

The second version sounds more expressive. It suggests that the second fact makes the situation even worse or more surprising.

In English, this often corresponds to stress like:

• He didn’t just ignore my request — he didn’t even open the letter.

So the sentence is not only grammatical information; it also carries rhetorical emphasis.