Le nom du destinataire n'est pas lisible sur l'enveloppe.

Du destinataire means of the recipient or of the addressee.

• destinataire = recipient / addressee
• du = de + le

So:

• le nom du destinataire = the recipient’s name / the name of the recipient

French often uses de where English would use ’s.

Because de + le contracts to du in French.

So:

• de + le → du
• de + les → des

Examples:

• le nom du destinataire
• la couleur du sac

You cannot normally say de le destinataire here.

French negation usually uses ne ... pas around the verb.

With être:

• est = is
• n'est pas = is not

The ne becomes n' before a vowel sound, so:

• ne est pas → n'est pas

This is called elision.

That is the normal French way to make a verb negative.

Pattern:

• ne ... pas

So:

• est = is
• n'est pas = is not

French usually places the negative in two parts around the conjugated verb.

In informal spoken French, people often drop ne, so you may hear:

• Le nom du destinataire est pas lisible

But in correct written French, use:

• Le nom du destinataire n'est pas lisible

Lisible means legible or readable.

In this sentence, it means the name can’t be read clearly on the envelope.

That is slightly more specific than visible:

• visible = visible, able to be seen
• lisible = readable, clear enough to read

So if handwriting is messy or smudged, lisible is the better word.

Because lisible is an adjective agreeing with nom, which is masculine singular.

• nom = masculine singular
• adjective used with it = lisible

Also, lisible has the same form in masculine singular and feminine singular:

• masculine singular: lisible
• feminine singular: lisible
• plural: lisibles

So there is no visible change here.

Sur l'enveloppe means on the envelope.

That makes sense because the recipient’s name is written on the outside surface of the envelope.

Compare:

• sur l'enveloppe = on the envelope
• dans l'enveloppe = in the envelope

If the name is written on the front of the envelope, sur is the natural choice.

Because la becomes l' before a vowel sound.

• la enveloppe is not used
• l'enveloppe is correct

This is another case of elision.

Also, enveloppe is a feminine noun:

• une enveloppe
• l'enveloppe

The sentence is built like this:

• Le nom du destinataire = subject
• n'est pas = verb in the negative
• lisible = adjective
• sur l'enveloppe = prepositional phrase giving location

So the pattern is basically:

[Subject] + [is not] + [adjective] + [location]

Very similar to English:

• The recipient’s name is not legible on the envelope.

Yes, you could.

• n'est pas lisible = is not legible
• est illisible = is illegible / unreadable

Both are correct, but there is a slight difference in tone:

• n'est pas lisible sounds a bit more neutral
• illisible can sound a bit stronger or more direct

In many contexts, they mean almost the same thing.

Usually yes, but in mail-related contexts destinataire is often best understood as addressee.

So in this sentence:

• le destinataire = the person the envelope is addressed to

A useful contrast is:

• destinataire = recipient / addressee
• expéditeur = sender

Nom literally means name, but in context it can refer to the name written for delivery purposes, often the person’s identifying name on the envelope.

Depending on context, English might translate it as:

• name
• recipient’s name
• sometimes even addressed name in a loose explanatory sense

It does not automatically mean full name, but it could include that in practice if the full name is what's written.

French usually expresses possession with de, not with an apostrophe.

So instead of:

• the recipient’s name

French says:

• le nom du destinataire
• literally: the name of the recipient

This is one of the most common differences between English and French sentence structure.