Я так и не смог открыть вложение и попросил переслать письмо ещё раз.

Так и не is an idiomatic pattern that adds the idea of in the end, it still didn’t happen or never did happen.

So:

Я не смог открыть вложение = I couldn’t open the attachment.
Я так и не смог открыть вложение = I never managed to open the attachment / I still couldn’t open it in the end.

It often suggests that the speaker expected the action to happen, or tried, but the result never came.

Very common 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 did meet.

Смог is the past tense of смочь, which is the perfective partner of мочь.

The difference is roughly:

• мог = could / was able to, in a general or ongoing sense
• смог = managed to / succeeded in being able to

In the negative:

• не мог открыть can mean was unable to open
• не смог открыть more strongly means did not manage to open

In this sentence, не смог fits well because the speaker is talking about a specific failed result: the attachment did not get opened.

Открыть is perfective, so it treats the action as a single complete result: to open successfully.

That works naturally after смог / не смог, because the point is whether the action was completed.

So:

• не смог открыть вложение = couldn’t manage to open the attachment

If you used открывать, it would sound more process-oriented or repeated, something like trying to open it in general or being engaged in the action.

After verbs like смочь, Russian very often uses a perfective infinitive when the result matters:

• смог найти
• не смог скачать
• смог отправить

In the Russian past tense, singular verbs show gender, not person.

So:

• смог, попросил = masculine
• смогла, попросила = feminine
• смогло, попросило = neuter

That means this sentence sounds like it is spoken by a male speaker.

If the speaker were female, it would be:

Я так и не смогла открыть вложение и попросила переслать письмо ещё раз.

Yes, it can sometimes be omitted, but Я is useful here because Russian past-tense verbs do not show person clearly.

For example:

• смог could mean I managed or he managed, depending on context
• смогла could mean I managed or she managed

So Я makes the subject explicit.

In conversation, if the subject is already obvious, Russian may drop it:

• Так и не смог открыть вложение и попросил переслать письмо ещё раз.

But as a standalone sentence, Я is natural and helpful.

Вложение is the normal Russian word for an attachment, especially an email attachment.

In this sentence it means the attached file.

Grammatically, it is the direct object of открыть, so it is in the accusative case. But because вложение is an inanimate neuter noun, its accusative form looks exactly like the nominative form:

• nominative: вложение
• accusative: вложение

The same thing happens with письмо later in the sentence.

This is a very common Russian structure:

попросить + infinitive = to ask someone to do something

So:

• попросил переслать письмо = asked to resend the email

Russian often omits the person being asked if it is already clear from context.

If you wanted to include that person, you could say:

• Я попросил коллегу переслать письмо ещё раз.
• Я попросил их переслать письмо ещё раз.

So the sentence does not mean the speaker personally resent it. It means the speaker requested that someone else resend it.

Because the speaker asked for the email to be sent again, not necessarily just the file by itself.

Переслать can mean forward or resend, depending on context. Here it most likely means resend/forward the email again.

Since the problem was with the attachment, asking for the whole email to be resent is very natural.

If the speaker specifically wanted only the file again, Russian could say:

• попросил переслать вложение ещё раз

Ещё раз means again or one more time.

So:

• переслать письмо ещё раз = resend the email again / one more time

It does not literally mean still once in English. As a fixed phrase, it simply means repetition.

Very common examples:

• Скажи ещё раз = Say it again.
• Попробуй ещё раз = Try again.
• Отправьте ещё раз = Send it again.

In the original sentence, it most naturally modifies переслать:

попросил переслать письмо ещё раз = asked for the email to be resent one more time

If you wanted to make it clearer that the speaker asked again, Russian would usually move ещё раз closer to попросил:

• ещё раз попросил переслать письмо

Russian word order is flexible, but position often helps show what is being emphasized.

Yes. In modern Russian, письмо can mean either a traditional letter or an email.

Context tells you which one is intended. Because this sentence includes вложение, the meaning is clearly email here.

So in everyday usage:

• получить письмо can mean receive a letter or receive an email
• отправить письмо can mean send a letter or send an email

Yes. Russian allows several natural versions of this idea.

For example:

• Я так и не смог открыть вложение и попросил переслать письмо ещё раз.
• Я так и не смог открыть вложение, поэтому попросил переслать письмо ещё раз.
• Я не смог открыть вложение и попросил ещё раз переслать письмо.

The original sentence is natural. Changing the word order mostly changes emphasis, not the basic meaning.