הבול אמור להיות על המעטפה לפני שאת מגיעה לסניף הדואר.

Hebrew usually does not use a separate present-tense verb for to be.

So הבול אמור להיות... is literally something like:

• the stamp supposed to be...

In natural English, we add is:

• The stamp is supposed to be...

This is very normal in Hebrew. In present-tense sentences, the copula is/am/are is often simply omitted.

Here אמור means supposed to, expected to, or sometimes meant to.

So הבול אמור להיות על המעטפה means:

• The stamp is supposed to be on the envelope
• or The stamp should be on the envelope

It is not exactly the same as a strong command. It sounds more like an expected or proper state.

Because אמור agrees with הבול, and בול is a masculine singular noun.

Agreement here is with the subject:

• הבול אמור = the stamp is supposed to...
• החבילה אמורה = the package is supposed to...

So the form changes according to the gender and number of the noun being described.

Because אמור is commonly followed by an infinitive.

Structure:

• אמור + infinitive

Examples:

• אני אמור ללכת = I am supposed to go
• הם אמורים להגיע = they are supposed to arrive
• הבול אמור להיות על המעטפה = the stamp is supposed to be on the envelope

Here the infinitive is להיות = to be, because the sentence is talking about the stamp being in a certain place.

Because a stamp goes on an envelope, not in it.

• על = on
• ב־ = in

So:

• על המעטפה = on the envelope
• במעטפה = in an envelope

This is just like English: you put a letter in an envelope, but a stamp on an envelope.

Because not all Hebrew prepositions combine with the definite article in the same way.

The short prepositions ב־, כ־, ל־ usually merge with ה־:

• ל + ה + סניף → לסניף
• ב + ה + בית → בבית
• כ + ה + ילד → כילד

But על usually stays separate:

• על המעטפה not a merged form

So this difference is normal Hebrew grammar:

• על המעטפה
• לסניף הדואר

לפני שאת means before you... when speaking to a female.

It breaks down like this:

• לפני = before
• ש־ = that / when / before, depending on context
• את = you (female singular)

So:

• לפני שאת מגיעה = before you arrive / before you get there

In modern Hebrew, לפני ש־ is a very common way to introduce a clause:

• לפני שאני הולך = before I go
• לפני שהם באים = before they come

Yes.

You can tell from:

• את = you, feminine singular
• מגיעה = arriving, feminine singular

So the speaker is talking to one woman.

If speaking to a man, it would be:

• לפני שאתה מגיע לסניף הדואר

If speaking to a group, the form would change again.

This is a good question, because both kinds of forms can appear in Hebrew.

Here מגיעה is the present-tense feminine singular form:

• את מגיעה = you arrive / you are arriving

In clauses with words like לפני ש־, Hebrew sometimes uses the present tense to talk about something future or expected, especially in general instructions or everyday speech.

So:

• לפני שאת מגיעה = before you arrive

A future form such as לפני שתגיעי can also be natural, and it may sound a bit more explicitly future-focused.

So the version in your sentence is normal, especially in practical instructions.

Because the verb להגיע usually takes the preposition ל־.

So Hebrew says:

• להגיע ל... = to arrive at / to get to ...

Examples:

• להגיע לבית = to arrive home / at the house
• להגיע לעיר = to arrive in the city
• להגיע לסניף הדואר = to arrive at the post office branch

Also, ל־ combines with the definite article ה־:

• ל + הסניף → לסניף

So לסניף is the expected form here.

סניף הדואר is a construct phrase, often called smikhut.

Literally it is:

• branch of the post/mail

Idiomatic meaning:

• the post office branch
• or simply the post office in this context

Hebrew often prefers this compact noun-noun structure instead of using של.

Compare:

• סניף הדואר = the post office branch
• הסניף של הדואר = the branch of the post office

Both can be understood, but the construct form is more standard and natural here.

Because in a construct phrase, the first noun usually does not take the definite article.

Definiteness comes from the second noun:

• סניף דואר = a post office branch
• סניף הדואר = the post office branch

Since הדואר is definite, the whole phrase becomes definite.

This is a very important Hebrew pattern:

• בית ספר = a school
• בית הספר = the school
• דלת הבית = the door of the house / the house door

Yes, it could, but the nuance would be a little different.

• הבול אמור להיות על המעטפה = the stamp is supposed to be on the envelope
• הבול צריך להיות על המעטפה = the stamp needs to be / should be on the envelope

אמור להיות often sounds like an expected condition or the proper situation.

צריך להיות sounds a bit more direct, like a requirement or necessity.

In many everyday situations, the two can be close in meaning, but they are not always identical in tone.