Не удаляй письмо: я ещё не сохранил вложение.

This is about aspect in the imperative.

• удалить = perfective: to delete/remove completely, as a completed action
• удалять = imperfective: to be deleting / to delete in general

In negative commands, Russian often prefers the imperfective:

• Не удаляй письмо = Don’t delete the email
• Не удалите письмо = more formal/plural version

Using не удаляй sounds natural for telling someone not to do the action.
If you said не удали, it would sound less neutral and more like make sure you don’t end up deleting it in a specific one-time sense.

So here не удаляй is the normal everyday choice.

Russian often leaves out subject pronouns when the verb already makes the subject clear.

• Не удаляй already means you (singular, informal) don’t delete
• я ещё не сохранил includes я, but Russian could sometimes omit it too if the context were clear

In this sentence, я is included for contrast and clarity:

• Don’t delete the email: I still haven’t saved the attachment

So Russian does not need to say ты here, because удаляй already shows that the speaker is talking to one person informally.

This is a very common point for English speakers.

Russian often uses the past tense of a perfective verb where English uses the present perfect.

• я не сохранил literally looks like I did not save
• but in context it means I haven’t saved it

Why? Because Russian does not have a separate tense exactly like the English present perfect. Instead, it expresses the result or non-result with aspect and context.

Here:

• сохранить = perfective, to save successfully / completely
• не сохранил = the saving has not been completed

Adding ещё gives the idea of not yet:

• я ещё не сохранил вложение = I haven’t saved the attachment yet

Here ещё means still or yet, depending on how you translate it into English.

In negative sentences like this, it often corresponds to yet:

• я ещё не сохранил = I haven’t saved it yet

More literally, it is something like:

• I still have not saved it

So ещё emphasizes that the action is expected to happen later, but has not happened so far.

In email/computer context, вложение means attachment.

• вложение = attachment, enclosed file
• приложение usually means application/app, or sometimes an appendix/addition in other contexts

So:

• вложение к письму = an attachment to an email
• приложение would usually be understood as an app/program, not an email attachment

That is why сохранил вложение is the natural phrase here.

Yes, письмо is the accusative singular here, because it is the direct object of удаляй.

• dictionary form: письмо = email/letter
• accusative singular: письмо

For neuter inanimate nouns like this, the nominative and accusative forms are the same, so the word does not change.

So:

• письмо пришло = the email arrived
• удаляй письмо = delete the email

Same form, different case function.

The colon links the command to the reason for it.

• Не удаляй письмо: я ещё не сохранил вложение.
• Don’t delete the email: I haven’t saved the attachment yet.

This is natural in Russian and English. The second part explains the first.

You could also say:

• Не удаляй письмо, я ещё не сохранил вложение.
• Не удаляй письмо, потому что я ещё не сохранил вложение.

But the colon is neat and clear: request first, explanation second.

Russian past tense verbs agree with the subject in gender when the subject is singular.

Here:

• я сохранил = said by a man
• я сохранила = said by a woman

So if a woman said the sentence, it would be:

• Не удаляй письмо: я ещё не сохранила вложение.

This is one of the things English speakers often notice quickly, because English past tense verbs do not change for gender.

Again, this is aspect.

• сохранить = perfective: to save successfully, to complete the saving
• сохранять = imperfective: to save, be saving, save repeatedly/habitually

In this sentence, the speaker is talking about whether the action has been completed, so Russian uses the perfective:

• я ещё не сохранил вложение = I have not completed saving the attachment yet

If you used сохранял, that would mean something different, more like:

• I wasn’t saving it
• I hadn’t been saving it
• or in some contexts I didn’t save it as an ongoing/process idea

So не сохранил is the correct choice when the focus is the missing result.

Yes. удаляй is the imperative for one person informally.

Polite/plural form:

• Не удаляйте письмо: я ещё не сохранил вложение.

So the forms are:

• удаляй = informal singular
• удаляйте = plural or polite singular

Everything else in the sentence can stay the same, except possibly сохранил / сохранила depending on the speaker’s gender.

It can mean either letter or email, depending on context.

In this sentence, because of вложение (attachment), it is most naturally understood as email:

• Не удаляй письмо = Don’t delete the email
• вложение strongly suggests a digital message

A physical letter would not normally have an attachment in this sense.

Yes, Russian word order is flexible, though different orders can change emphasis.

Neutral version:

• Не удаляй письмо: я ещё не сохранил вложение.

Possible variations:

• Я ещё не сохранил вложение, не удаляй письмо.
  This puts the reason first, then the request.

• Вложение я ещё не сохранил, не удаляй письмо.
  This emphasizes the attachment.

The original sentence is natural because it gives:

1. the urgent instruction
2. the reason

That makes perfect sense in conversation.