Из-за рассеянности я вчера так и не смог толком дочитать письмо.

Из-за means because of, due to, or sometimes as a result of.

After из-за, Russian normally uses the genitive case, so:

• рассеянность = absent-mindedness, inattentiveness
• из-за рассеянности = because of absent-mindedness

This is a fixed prepositional pattern:

• из-за дождя = because of the rain
• из-за работы = because of work
• из-за рассеянности = because of absent-mindedness

So the genitive here is required by из-за.

Рассеянность usually means absent-mindedness, scatterbrained behavior, or lack of concentration/attention.

Depending on context, it can suggest:

• being mentally distracted
• not focusing properly
• being forgetful or unfocused

So in this sentence, it suggests the speaker could not properly finish reading the letter because they were too distracted or absent-minded.

It is a noun formed from the adjective рассеянный, which can mean:

• absent-minded
• distracted
• scatterbrained

Так и не смог adds emphasis. It means something like:

• still couldn’t
• never managed to
• ended up not being able to
• just couldn’t, in the end

Compare:

• Я не смог дочитать письмо.
  = I couldn’t finish reading the letter.

• Я так и не смог дочитать письмо.
  = I never did manage to finish reading the letter.

The combination так и не + verb often expresses an expected result that never happened.

Examples:

• Я так и не позвонил. = I never did call.
• Он так и не пришёл. = He never ended up coming.

So here it gives a stronger sense of failure to complete something.

Смог is the masculine singular past tense of смочь, which is the perfective partner of мочь (to be able to / can).

So:

• мочь = to be able, can
• смочь = to manage to, succeed in being able to

In this sentence, смог fits well because the speaker is talking about a specific completed situation in the past: whether they managed to finish reading the letter or not.

That is why Russian often prefers смочь in cases like this:

• Я не мог = I was not able / couldn’t
• Я не смог = I failed to manage to

Here не смог is very natural because it focuses on the failed outcome.

After verbs meaning can / be able / manage, Russian often uses an infinitive:

• смог сделать = managed to do
• не смог прийти = couldn’t come
• не смог дочитать = couldn’t finish reading

So the structure is:

• смог = managed / was able
• дочитать = to finish reading

Together:

• не смог дочитать письмо = could not finish reading the letter

This is very normal Russian grammar.

Дочитать means to read through to the end, to finish reading something that has already been started.

That is the key nuance.

Compare:

• читать письмо = to read a letter / be reading a letter
• прочитать письмо = to read a letter completely
• дочитать письмо = to finish reading the rest of the letter

So дочитать implies that the person had already started reading it but did not manage to get to the end.

That works very naturally with the context:

• they were reading the letter
• because of absent-mindedness, they could not properly finish it

Толком means something like:

• properly
• really
• in a satisfactory way
• with full understanding / attention

In this sentence, толком дочитать письмо suggests not just mechanically reaching the last line, but reading it properly and attentively.

Some similar examples:

• Я ничего толком не понял. = I didn’t really understand anything properly.
• Мы толком не поговорили. = We didn’t really have a proper talk.
• Он толком не объяснил. = He didn’t explain it properly.

So here толком strengthens the idea that the reading was unsuccessful in a meaningful way.

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

The dictionary form is:

• письмо = letter

For neuter inanimate nouns, the accusative singular is the same as the nominative singular, so the form does not change:

• nominative: письмо
• accusative: письмо

That is why it looks unchanged.

Yes, вчера can move around. Russian word order is flexible, and changing the order mainly changes emphasis, not the basic meaning.

This version:

• Из-за рассеянности я вчера так и не смог толком дочитать письмо.

sounds natural and neutral. It presents:

1. the reason
2. the subject
3. the time
4. the failed result

Other possible orders:

• Вчера я из-за рассеянности так и не смог толком дочитать письмо.
• Я так и не смог вчера толком дочитать письмо.
• Я вчера из-за рассеянности так и не смог толком дочитать письмо.

All are possible, but the original sounds smooth and idiomatic.

Yes, Russian often drops personal pronouns when the subject is clear from the verb form.

So you could say:

• Из-за рассеянности вчера так и не смог толком дочитать письмо.

and it would still be understood as I from смог if the speaker is male, or смогла if female.

But including я is also normal. It can make the sentence slightly clearer or more personal:

• Из-за рассеянности я вчера...

So both versions are natural.

Yes, as written, смог implies a male speaker.

In the past tense, Russian verbs agree with gender in the singular:

• я смог = I managed / could (male speaker)
• я смогла = I managed / could (female speaker)

So if the speaker were female, the sentence would be:

• Из-за рассеянности я вчера так и не смогла толком дочитать письмо.

Из-за often has a slightly negative flavor, especially when talking about problems, obstacles, or unwanted causes.

For example:

• из-за пробок = because of traffic jams
• из-за ошибки = because of a mistake
• из-за рассеянности = because of absent-mindedness

That makes it a good fit here, because the cause is something that prevented success.

For more neutral causes, Russian sometimes uses:

• из-за if the cause is seen as troublesome
• из / от / other expressions in different contexts

So here из-за sounds very natural because the absent-mindedness caused a negative result.

A fairly literal breakdown is:

• Из-за рассеянности = Because of absent-mindedness
• я = I
• вчера = yesterday
• так и не смог = never did manage / ended up not being able
• толком = properly
• дочитать письмо = to finish reading the letter

So the sentence is built like this:

Because of absent-mindedness, I yesterday never did manage to properly finish reading the letter.

That is not natural English word order, but it shows how the Russian pieces fit together.