Jutro odeślę przesyłkę zwrotną.

Because odeślę is the perfective verb form, and in Polish perfective verbs often use a simple future form.

• odesłać = to send back, to dispatch back once, as a completed action
• odeślę = I will send back

By contrast:

• odsyłać = to be sending back / to send back repeatedly or in an ongoing sense
• będę odsyłać = I will be sending back / I will send back (imperfective)

In this sentence, the speaker means one completed future action, so odeślę is the most natural choice.

The infinitive is odesłać.

This verb can be tricky because the stem changes:

• infinitive: odesłać
• 1st person singular future: odeślę

That change is normal for this verb. It is similar to other Polish verbs with stem changes in conjugation.

In Polish, perfective verbs do not have a present tense with present meaning. Their present-tense-looking forms are used to express the future.

So:

• odeślę literally looks like a present-form pattern
• but because odesłać is perfective, odeślę means I will send back

This is a very common feature of Polish verbs.

Because Polish usually drops subject pronouns when they are clear from the verb ending.

• odeślę already means I will send back
• the ending -ę tells you the subject is I

You could say Ja jutro odeślę przesyłkę zwrotną, but ja would add emphasis, like I will send it back.

Because this phrase is the direct object of the verb, so it has to be in the accusative case.

The dictionary form is:

• przesyłka zwrotna

But after a transitive verb like odeślę, it changes to accusative:

• przesyłkę zwrotną

Both words are feminine singular, so both change:

• przesyłka → przesyłkę
• zwrotna → zwrotną

The dictionary form is przesyłka, and nouns ending in -a are very often feminine in Polish.

You can also see that the adjective agrees with it:

• nominative: przesyłka zwrotna
• accusative: przesyłkę zwrotną

That feminine agreement is a strong clue.

Here zwrotną means return or being sent back.

It comes from zwrotny, which can mean things like:

• return
• reciprocal
• reflexive
• reversible

But in this context, przesyłka zwrotna is a set phrase meaning a return parcel/shipment.

So this is not the everyday adjective returned in a random sense; it is specifically the kind of parcel that is being sent back.

In Polish, adjectives often come before the noun, but some combinations commonly have the adjective after the noun, especially in more formal, technical, or established expressions.

So:

• przesyłka zwrotna sounds like a standard term
• it is similar to other fixed expressions where the adjective follows the noun

Putting the adjective before the noun might still be understandable, but przesyłka zwrotna is the more natural established phrase.

Yes. Polish word order is relatively flexible.

All of these are possible:

• Jutro odeślę przesyłkę zwrotną.
• Odeślę jutro przesyłkę zwrotną.
• Przesyłkę zwrotną odeślę jutro.

The basic meaning stays the same, but the emphasis changes:

• Jutro first emphasizes tomorrow
• Przesyłkę zwrotną first emphasizes the parcel
• Odeślę first can sound more action-focused

The original sentence is very natural if the main new information is when the action will happen.

No. Jutro can appear in different positions.

Examples:

• Jutro odeślę przesyłkę zwrotną.
• Odeślę przesyłkę zwrotną jutro.
• Przesyłkę zwrotną odeślę jutro.

Beginning position is very common because time expressions often come early in the sentence, especially when they set the scene.

A careful pronunciation guide would be roughly:

• o-de-shlę

More precisely:

• ś sounds like a soft sh
• lę here is pronounced with ę, a nasal vowel

The tricky part is the cluster śle. Try saying it as one smooth unit, something like shle but with a softer sh sound.

Also, Polish stress is usually on the second-to-last syllable, so:

• o-DE-ślę

They overlap, but they are not identical.

• przesyłka = shipment, consignment, mailed item; broader and more formal/logistical
• paczka = package, parcel; very common everyday word
• pakiet = package, bundle, packet; often for a set of things, services, or documents

So przesyłka zwrotna sounds more like postal/logistics language than paczka zwrotna, although the latter may also be understandable in everyday speech depending on context.

Yes, potentially. Przesyłka is broader than paczka.

It can mean a mailed or shipped item in general, depending on context:

• a parcel
• a shipment
• a postal item

So without extra context, przesyłkę zwrotną does not have to mean only a box or parcel. It can be any returned shipment/item.

Usually no, not in the same sense.

• odeślę = I will send back
• oddam = I will give back / return

Use odeślę when the item is being sent, mailed, or dispatched back. Use oddam when you physically give something back.

So if you are talking about sending a return package through the post or courier, odeślę is the right verb.