El establecimiento y la mensajería abren mañana.

Because the subject is two things: el establecimiento + la mensajería.

In Spanish, when two singular nouns are joined by y and both are the subject, the verb normally goes in the plural:

• El establecimiento abre mañana.
• La mensajería abre mañana.
• El establecimiento y la mensajería abren mañana.

So abren agrees with the whole plural subject.

Spanish often repeats the article before each noun when talking about separate, distinct items.

So:

• el establecimiento y la mensajería

sounds natural because it clearly presents two different entities.

If you removed the second article, the phrase would feel less natural here and could sound like the two nouns are being grouped more tightly than intended. In this sentence, using both articles is the normal, clear choice.

Usually, no.

In Spain, mensajería often means a courier service, delivery service, or the shop/business that handles parcels and deliveries. It is not usually the everyday word for phone or chat messaging by itself.

For digital messaging, Spanish would more often say things like:

• mensajes
• mensajería instantánea

So la mensajería here is most naturally understood as a courier/delivery business.

Because mañana meaning tomorrow works as a time adverb, and in Spanish time adverbs often appear on their own:

• Hoy
• Mañana
• Ayer

So abren mañana is perfectly normal.

By contrast, if you want to say in the morning, Spanish usually uses:

• por la mañana

So there is a big difference between:

• abren mañana = they open tomorrow
• abren por la mañana = they open in the morning

In this sentence, it is understood as tomorrow.

The word mañana can be a noun meaning morning, but when Spanish means morning in a time expression, it usually says:

• por la mañana

So:

• El establecimiento y la mensajería abren mañana = tomorrow
• El establecimiento y la mensajería abren por la mañana = in the morning

If you wanted to say tomorrow morning, you could say:

• abren mañana por la mañana

Because Spanish very often uses the present tense for scheduled, planned, or near-future events.

So abren mañana is a normal way to say that they are opening tomorrow.

English does something similar:

• They open tomorrow.

Spanish could also use the future:

• abrirán mañana

But abren mañana often sounds more direct and natural, especially for schedules, business hours, and planned openings.

Yes, but it sounds a bit general or formal.

Establecimiento means something like a business premises, shop, or establishment. It is common in formal language, notices, regulations, or business contexts.

In more casual everyday speech, people might instead say:

• tienda if it is a shop
• local if referring to the premises
• comercio for a business/shop in a more general sense

So establecimiento is correct and natural, but it is a somewhat broad, neutral term.

Yes, Spanish word order is flexible, but the original order is very clear.

You could say:

• Mañana, el establecimiento y la mensajería abren.

That is understandable, though a little more marked in style.

However, be careful with:

• Mañana abren el establecimiento y la mensajería.

That version can sound ambiguous, because abren can also mean they open something, so a listener might first understand el establecimiento y la mensajería as the objects of the verb rather than the subject.

So El establecimiento y la mensajería abren mañana is a very clear and safe wording.

Because y is the normal Spanish word for and.

Spanish changes y to e only before words that begin with an i- or hi- sound, to avoid an awkward repetition of the same sound:

• padre e hijo
• España e Italia

But mensajería begins with an m sound, so the normal form is:

• el establecimiento y la mensajería