Στα εισερχόμενα βρήκα το μήνυμα της γραμματείας και ένα συνημμένο με τη νέα φόρμα.

Στα is the contracted form of σε + τα.

• σε = in / at / to
• τα = the for neuter plural nouns

So στα εισερχόμενα literally means in the incoming things, but in modern usage it means in the inbox.

Greek very often combines σε with the definite article:

• σε + το = στο
• σε + τη(ν) = στη(ν)
• σε + τα = στα

Because Greek uses τα εισερχόμενα as a set expression for incoming mail/messages.

Grammatically, εισερχόμενα is a neuter plural form originally related to things coming in. Greek often uses plural forms for categories or folders like this, for example:

• τα εισερχόμενα = inbox
• τα εξερχόμενα = outbox / outgoing mail

So even though English uses the singular word inbox, Greek commonly uses this plural expression.

Βρήκα is the aorist of βρίσκω and means I found.

The aorist is used for a single completed action in the past. Here, the speaker is talking about one finished event: they checked the inbox and found something.

So:

• βρίσκω = I find / I am finding
• βρήκα = I found

An English speaker can think of it as the normal simple past in this sentence.

Because Greek usually does not need subject pronouns when the verb ending already shows who the subject is.

In βρήκα, the ending tells you it is first person singular: I found.

So εγώ βρήκα is possible, but it would usually add emphasis, something like:

• I found it

Without εγώ, the sentence sounds natural and neutral.

Της γραμματείας is in the genitive case.

It depends on το μήνυμα and shows whose message it is, or where it comes from:

• το μήνυμα της γραμματείας = the message of the office / the message from the office

For English speakers, this genitive is often translated as either:

• of the ...
• from the ...

depending on what sounds more natural in English.

Also, γραμματεία can mean things like:

• office
• administration
• secretariat
• in schools/universities, often the registrar’s office or the department office

Because συνημμένο can function as a noun by itself, just like English attachment.

Originally it is an adjective/participle meaning attached, but in modern Greek it is very commonly used on its own to mean:

• an attachment
• attached file

So ένα συνημμένο is completely natural Greek and does not need another noun after it.

Most naturally, it describes ένα συνημμένο.

So the structure is understood as:

• I found the message from the office and an attachment with the new form

In other words, the attachment contains or includes the new form.

Could με τη νέα φόρμα theoretically be read with το μήνυμα? In isolation, maybe. But in this sentence, the closest and most natural connection is with ένα συνημμένο.

After the preposition με (with), Greek uses the accusative case.

So:

• τη φόρμα = accusative singular feminine
• νέα agrees with φόρμα, so it is also feminine singular accusative

That is why you get:

• με τη νέα φόρμα

A few grammar points are working together here:

• με
  • accusative
• τη = feminine singular accusative article
• νέα = adjective agreeing with φόρμα
• φόρμα = feminine singular noun

So the whole phrase is grammatically matched.

In modern Greek, the final -ν of την is often dropped before certain consonants.

Since νέα begins with ν, the usual everyday form is:

• τη νέα φόρμα

This is normal and standard.

Very roughly:

• before vowels and some consonants, Greek often keeps the final -ν
• before others, it usually drops it

So here τη νέα is the expected form.

Greek word order is fairly flexible, but the version here is natural because it starts with the location/context:

• Στα εισερχόμενα = In the inbox

Then it gives the main action:

• βρήκα = I found

Then it gives what was found:

• το μήνυμα της γραμματείας και ένα συνημμένο με τη νέα φόρμα

Starting with Στα εισερχόμενα helps set the scene first. A different order is also possible, for example:

• Βρήκα στα εισερχόμενα το μήνυμα της γραμματείας και ένα συνημμένο με τη νέα φόρμα.

That is also grammatical, but the original version sounds a bit more natural if you want to emphasize where you found them.