К сожалению, письмо снова попало в спам, хотя отправитель написал правильный адрес.

К сожалению means unfortunately or literally to regret / to [someone’s] regret.

In this sentence, it functions like a parenthetical introductory phrase: it comments on the whole statement rather than acting as a normal part of the clause. Because of that, it is usually set off with a comma:

К сожалению, письмо снова попало в спам...

This is very common in Russian with expressions like:

• К счастью, ... — fortunately
• По-моему, ... — in my opinion
• Наверное, ... — probably

So the comma is not random punctuation; it marks an introductory expression.

Because the subject is письмо (letter / email), and письмо is a neuter noun in Russian.

In the past tense, Russian verbs agree with the subject in gender and number:

• masculine: попал
• feminine: попала
• neuter: попало
• plural: попали

So:

• письмо попало — the letter/email ended up
• письма попали — the letters/emails ended up

Even though an email is not physically moving anywhere, Russian uses this verb naturally in this context.

Here попало comes from попасть, which often means to get into, to end up in, or to land in.

So письмо попало в спам literally means:

• the email got into spam
• the email ended up in the spam folder

This is a very natural Russian way to talk about email filtering.

A useful pattern is:

• попасть в спам — to end up in spam
• попасть в аварию — to get into an accident
• попасть в список — to get onto a list

So the core idea is: something ends up somewhere, often as a result.

Because попасть expresses movement into a place/state/result, and after verbs of motion or entry, Russian often uses в + accusative.

So:

• в спам = into spam
• в папку = into the folder
• в список = onto/into the list

By contrast, в спаме would be in spam, describing location rather than movement/result.

Compare:

• Письмо попало в спам. — The email went into spam.
• Письмо уже в спаме. — The email is already in spam.

Here, the sentence is about the result of ending up there, so в спам is correct.

It actually is in the accusative, but for this noun the accusative looks the same as the nominative.

спам is a masculine inanimate noun, and for most masculine inanimate nouns:

• nominative = accusative

So:

• nominative: спам
• accusative: спам

That is why after в you still see спам with no visible ending change.

The same thing happens with words like:

• в парк — into the park
• в список — into the list
• в архив — into the archive

Снова means again.

In this sentence:

письмо снова попало в спам
= the email ended up in spam again

Its position is flexible, but where you place it can affect emphasis slightly. For example:

• Письмо снова попало в спам. — neutral; the email again ended up in spam
• Снова письмо попало в спам. — more marked; emphasis on again
• Письмо попало снова в спам. — possible, but less natural than the first version

Russian word order is more flexible than English, but not completely free. The given order is the most natural neutral one.

Хотя means although, even though, or sometimes though.

It introduces a subordinate clause:

..., хотя отправитель написал правильный адрес.
= ..., although the sender wrote the correct address.

Russian normally puts a comma before хотя when it introduces this kind of clause, just as English separates although-clauses in writing.

So the sentence has two parts:

1. письмо снова попало в спам
2. хотя отправитель написал правильный адрес

The second part contrasts with the first: even though the address was correct, the email still went to spam.

Отправитель means sender and is the subject of the second clause.

It is in the nominative case, because it is the person doing the action:

• отправитель написал — the sender wrote

The verb написал is masculine singular past tense, which agrees with отправитель, a masculine noun.

If the subject were feminine, the verb would change:

• отправительница написала — the female sender wrote

So this is standard subject-verb agreement in the past tense.

This is about aspect, which is very important in Russian.

• писать = imperfective
• написать = perfective

Написал presents the action as completed: the sender entered/wrote the correct address successfully.

That fits the meaning here, because the sentence refers to a finished result: the address was indeed written correctly.

Compare:

• отправитель писал адрес — the sender was writing the address / used to write the address
• отправитель написал адрес — the sender wrote the address

In this sentence, Russian wants the completed action, so написал is the natural choice.

Правильный адрес is in the accusative case, because it is the direct object of написал:

• написал что? — wrote what?
• правильный адрес

However, because адрес is a masculine inanimate noun, its accusative singular looks exactly like the nominative singular:

• nominative: правильный адрес
• accusative: правильный адрес

That is why there is no visible ending change here.

Compare with a feminine noun, where you would see a change:

• написал правильную улицу — wrote the correct street name

So the object is accusative, even if the form looks unchanged.

It is understandable and correct, but depending on context, Russian speakers might also say:

• указал правильный адрес — indicated/provided the correct address
• ввёл правильный адрес — entered the correct address
• написал адрес правильно — wrote the address correctly

Why? Because with email, написать адрес can sound like physically writing or typing the address, while указать or ввести may sound more specific for forms, email fields, or online systems.

Still, написал правильный адрес is perfectly acceptable, especially if the idea is simply that the sender did not make a mistake in the address.

Literally, письмо can mean either:

• a letter
• an email

In this sentence, because of попало в спам, it clearly means email.

Russian often uses the same word письмо for both traditional letters and email messages, and the context tells you which one is meant.

For example:

• Я получил письмо. — I got a letter / email
• Письмо пришло на почту. — often understood as an email arriving in your inbox
• Письмо попало в спам. — definitely an email

So this is a normal Russian use of письмо.

Russian word order is flexible, but different orders sound more or less natural depending on emphasis.

The original sentence is a very natural neutral version:

К сожалению, письмо снова попало в спам, хотя отправитель написал правильный адрес.

Possible variations include:

• К сожалению, снова письмо попало в спам...
  More emphasis on again, but less neutral.

• Письмо, к сожалению, снова попало в спам...
  Also natural; к сожалению is inserted into the clause.

• Хотя отправитель написал правильный адрес, письмо снова попало в спам.
  This puts the contrast clause first: Although the sender wrote the correct address, ...

So yes, the order can change, but the original is probably the best default version for everyday neutral Russian.