Перешли мне файл ещё раз, пожалуйста: я так и не смог открыть вложение.

Yes. Перешли here is the informal singular imperative of переслать / переслать? Actually, the verb is переслать or its colloquial variant переслать / пересылать pair, and перешли means resend / send again / forward to one person informally.

So:

• Перешли мне файл = Resend me the file
• Перешлите мне файл = formal or plural Please resend me the file

This form can look confusing because перешли can also be a past tense plural form of other verbs, but here the meaning and context clearly show it is an imperative.

Because мне is the dative case, used for the person who receives something.

• я = I
• мне = to me

In Russian, with verbs like дать (give), послать (send), переслать (resend), the recipient is usually in the dative:

• Отправь мне письмо = Send me the letter
• Перешли мне файл = Resend me the file

So мне means to me, even though in natural English we usually just say send me.

It is in the accusative. The reason it looks unchanged is that файл is:

• masculine
• inanimate
• singular

For many masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• nominative: файл
• accusative: файл

That is why Перешли мне файл looks the way it does.

Compare with an animate noun:

• Я вижу брата = I see my brother

There, the accusative changes form.

Ещё раз means again, one more time, or once more.

In this sentence:

• Перешли мне файл ещё раз = Resend me the file again / one more time

It is a very common phrase in Russian:

• Скажи ещё раз = Say it again
• Повтори ещё раз = Repeat it once more
• Прочитай ещё раз = Read it again

Here it makes it clear the file was sent before, but the speaker wants it sent again.

Так и не is a very common Russian pattern that adds emphasis. It means something like:

• never did
• still didn’t
• ended up not being able to
• failed to, despite expectation

So:

• я не смог открыть вложение = I couldn’t open the attachment
• я так и не смог открыть вложение = I still couldn’t open the attachment / I never managed to open the attachment

The phrase suggests that the speaker probably tried, or was expected to succeed, but in the end it did not happen.

Other examples:

• Я так и не понял = I never did understand
• Он так и не пришёл = He never ended up coming
• Мы так и не встретились = We never managed to meet

This is a very useful expression to learn.

Because смог открыть means managed to open / was able to open, not just opened.

Compare:

• Я не открыл вложение = I didn’t open the attachment
  This only states that the opening did not happen.
• Я не смог открыть вложение = I couldn’t open / I wasn’t able to open the attachment
  This tells you there was an attempt or possibility, but something prevented success.

So смочь + infinitive is used when Russian wants to express ability or managing to do something.

In this sentence, that is important: the speaker is explaining why they want the file resent. The issue is not just that they didn’t open it; it is that they couldn’t.

Because открыть is the perfective infinitive, and after смочь Russian often uses the infinitive that matches the specific completed action someone was or was not able to do.

• открыть = to open successfully, as a complete action
• открывать = to be opening / to open repeatedly / to open in a more ongoing sense

Here the speaker means:

• I couldn’t open the attachment
  = I wasn’t able to complete that action

So смог открыть is the natural choice.

Вложение is in the accusative singular, because it is the direct object of открыть.

• открыть что? = to open what?
• вложение = attachment

Like many neuter inanimate nouns, its accusative singular looks exactly like the nominative singular:

• nominative: вложение
• accusative: вложение

So the form does not visibly change, but grammatically it is accusative.

Here вложение means attachment, especially an email attachment.

More literally, it comes from the idea of something enclosed or inserted.

In modern everyday Russian, вложение is very commonly used for email attachments:

• открыть вложение = open the attachment
• отправить письмо с вложением = send an email with an attachment

Depending on context, it can also mean an enclosure in a broader sense, but in this sentence email attachment is definitely the intended meaning.

The colon introduces the reason or explanation for the request.

So the structure is:

• Перешли мне файл ещё раз, пожалуйста:
  я так и не смог открыть вложение.

This is similar to English punctuation in a sentence like:

• Please resend the file: I couldn’t open the attachment.

In English, many people might prefer a period, dash, or because, but in Russian a colon is a natural way to connect a request with the explanation for it.

Yes, пожалуйста can move around somewhat.

In this sentence:

• Перешли мне файл ещё раз, пожалуйста

it softens the request and means please.

Possible variants include:

• Пожалуйста, перешли мне файл ещё раз.
• Перешли, пожалуйста, мне файл ещё раз.
• Перешли мне, пожалуйста, файл ещё раз.

All are understandable. The version in your sentence sounds natural and conversational.

Russian word order is flexible, and moving пожалуйста usually changes rhythm or emphasis more than basic meaning.

Yes. Перешли is informal singular: you are speaking to one person you address as ты.

Polite or plural forms:

• Перешлите мне файл ещё раз, пожалуйста. = Please resend me the file.
  This can mean:
  • speaking politely to one person (вы)
  • speaking to more than one person

So the distinction is:

• перешли = informal singular
• перешлите = formal singular or plural

Yes. In the past tense, Russian verbs show gender in the singular.

• смог = masculine
• смогла = feminine
• смогло = neuter
• смогли = plural

So я так и не смог открыть вложение suggests that the speaker is male, or that the sentence is being given in a default dictionary-style form. If the speaker were female, it would usually be:

• Я так и не смогла открыть вложение.

This is something English speakers often notice, since English past tense does not show gender.

Sometimes yes, depending on context, but resend is the safer default here.

The verb переслать can mean:

• resend
• forward

The exact meaning depends on the situation:

• If the same sender is sending the file again because the first attempt failed, resend fits best.
• If someone is passing along a file they received from someone else, forward may fit.

Because the second half mentions I couldn’t open the attachment, the most natural reading is that the file was already sent to the speaker once and they want it sent again. So resend is probably best here.