Сначала я проверю вложение, а потом уже отправлю письмо.

Because Russian often builds the future directly into the verb form.

Here, проверю is the 1st person singular future of проверить, and отправлю is the 1st person singular future of отправить.

A key rule is:

• Perfective verbs form the future with simple personal endings.
• Imperfective verbs usually form the future with буду + infinitive.

So:

• проверю = I will check
• отправлю = I will send

These look like present-tense forms, but with perfective verbs they are understood as future, because perfective verbs do not have a true present tense.

Because the sentence describes two single completed actions in sequence:

1. check the attachment
2. send the message

The speaker is not talking about the process in general, but about getting each step done.

So:

• проверю suggests I will check it and finish checking it
• отправлю suggests I will send it off

If you used imperfective forms such as буду проверять or буду отправлять, the focus would shift more toward the process, duration, or repeated action. That would sound less natural for this kind of simple step-by-step plan.

Here уже does not simply mean already in the basic textbook sense.

In this sentence, it adds a nuance like:

• and only then
• and after that
• and then, once that’s done

So а потом уже отправлю письмо means something like and only after that will I send the email.

Without уже, the sentence would still be correct:

Сначала я проверю вложение, а потом отправлю письмо.

But with уже, the order feels a little more deliberate and emphasized.

In Russian, а often connects two parts that are being set against each other or presented as separate stages.

Here it marks a transition from step 1 to step 2:

• first I’ll do this,
• and then I’ll do that.

So сначала ..., а потом ... is a very common pattern.

Using и is not impossible in all contexts, but а потом is the more natural choice when you are clearly moving from one stage to the next.

Because а joins two clauses:

• Сначала я проверю вложение
• а потом уже отправлю письмо

Russian normally uses a comma before а when it connects clauses like this.

Even though the subject я is not repeated in the second clause, the second part still has its own verb, so the comma is needed.

They are objects, so they are in the accusative case.

However, for neuter inanimate singular nouns, the accusative looks exactly the same as the nominative.

That is why you see:

• вложение
• письмо

with no visible change.

So in this sentence:

• проверю вложение = direct object in accusative
• отправлю письмо = direct object in accusative

The form just happens to be identical to the basic dictionary form.

Russian has no articles, so it does not directly mark the difference between a/an and the.

That distinction comes from context.

In a sentence like this, English usually says the attachment and the email if both speaker and listener already know which ones are meant. But Russian itself does not show that with an article.

So вложение and письмо are article-neutral on their own.

It can mean either, depending on context.

Traditionally, письмо means letter, but in modern usage it is also very common for email, especially in work or computer-related contexts.

In this sentence, вложение strongly suggests an email context, because attachments are normally attached to emails. So the most likely meaning here is email.

If someone wanted to be extra explicit, they might say:

• электронное письмо = email
• email = email

But письмо by itself is very normal.

Because Russian often leaves out a repeated subject when it is already clear.

In this sentence, the subject of both verbs is the same person: I.

So after я проверю, Russian does not need to repeat я before отправлю, because the verb ending -ю already shows 1st person singular.

You could repeat it:

Сначала я проверю вложение, а потом я уже отправлю письмо.

But that usually sounds more emphatic. The version without the second я is more natural and smoother.

Yes. Russian word order is flexible, and changing it often changes emphasis rather than basic meaning.

The given sentence is a very natural neutral order:

Сначала я проверю вложение, а потом уже отправлю письмо.

Possible variations include:

• Сначала проверю вложение, а потом уже отправлю письмо.
• Вложение сначала проверю, а потом уже отправлю письмо.
• А потом уже отправлю письмо, но сначала проверю вложение.

These all keep the same general idea, but the focus shifts slightly.

For a learner, the original version is a good model because it is clear, standard, and idiomatic.