Mi ne resendos ĝin sen ke klientservo sendos etikedon kaj spurkodon.

It breaks down like this:

• sendi = to send
• re- = again / back
• -os = future tense

So resendos means will resend or will send back, depending on context.

That -os ending is the key grammar point: it tells you the action is in the future.

Because ĝin is the direct object form.

• ĝi = it, as a subject
• ĝin = it, as an object

Compare:

• Ĝi alvenis. = It arrived.
• Mi resendos ĝin. = I will resend it.

Esperanto marks direct objects with -n, including pronouns.

Both words are direct objects of sendos.

Customer service is sending two things:

• etikedon = a label
• spurkodon = a tracking code

In Esperanto, each direct object keeps its own -n, even when joined by kaj.

So:

• sendos etikedon kaj spurkodon

means that both things are being sent.

Literally, sen ke means something like without it being the case that.

In this sentence, because the main clause is negative:

• Mi ne resendos ĝin sen ke ...

it works a lot like English I won’t resend it unless ...

So the structure is essentially:

• not ... without ...
• which often corresponds to not ... unless ...

It is understandable, but many Esperanto speakers would more directly use krom se for unless.

A very natural version would be:

• Mi ne resendos ĝin, krom se klientservo sendos etikedon kaj spurkodon.

So:

• sen ke = literally without that
• krom se = more directly unless

The original sentence is understandable, but krom se is often the clearest choice.

That is a very common English-speaker question.

Esperanto does not follow the same tense rule as English here. In Esperanto, if the action is future from the speaker’s point of view, using the future tense is normal:

• klientservo sendos = customer service will send

English often uses present tense after words like if, when, and unless, but Esperanto does not have to copy that pattern.

So sendos is understandable and grammatically possible.

Yes, and many learners will see or hear that kind of wording.

• sendos states a future event
• sendu presents it more as a requirement, condition, or expected action

So these feel slightly different:

• sen ke klientservo sendos ... = without customer service sending / before customer service will send
• sen ke klientservo sendu ... = unless customer service first send / without customer service being made to send

In practice, with sen ke, many speakers may prefer sendu, because the clause feels conditional rather than purely factual.

So if you keep sen ke, sendu may sound more idiomatic to some speakers.

Because the second action has a different subject.

Here:

• Mi = the person who will resend it
• klientservo = the one who will send the label and tracking code

When the subject changes, Esperanto often uses a full clause:

• sen ke klientservo sendos/sendu ...

If the subject were the same, a shorter structure might work:

• Mi ne foriros sen pagi. = I will not leave without paying.

But in your sentence, I am not the one doing the sending of the label and tracking code, so a full clause is needed.

Because Esperanto very often forms compound words.

• kliento = customer
• servo = service

Together:

• klientservo = customer service

This is very normal in Esperanto. Instead of separate words, Esperanto often combines roots into one compound noun.

The same thing happens in:

• spurkodo = tracking code
• poŝtelefono = mobile phone
• retpaĝo = webpage

Esperanto uses la only when you want to mark something as definite.

In a sentence like this, omitting la can sound like referring to customer service as a department or function in a general business context:

• klientservo

If you want to emphasize a specific known customer service department, la klientservo could also be possible.

So the choice is partly contextual:

• klientservo = customer service, as a department/service
• la klientservo = the customer service department, a specific one already understood from context

Both can make sense, depending on what the speaker wants to emphasize.