أرسلت الرسالة للتو.

A fully vocalized version is:

أرسلتُ الرسالةَ للتوِّ.

In careful pronunciation, that is roughly arsaltu ar-risālata lit-tawwi. In normal pause, the final short vowels are often not pronounced.

Because the verb already tells you the subject.

In أرسلتُ, the ending ـتُ means I. Arabic often leaves subject pronouns unstated when the verb form already makes them clear.

You can say أنا أرسلتُ الرسالةَ للتوِّ if you want extra emphasis on I, but it is not required.

Yes. In unvowelled writing, أرسلت can be ambiguous.

• أرسلتُ = I sent
• أرسلتْ = she sent

Context usually makes it clear.

Also, a male speaker and a female speaker both say أرسلتُ for I sent. In first person singular, Arabic does not change the verb for the speaker’s gender.

Because Arabic normally uses the perfect/past form for a completed action, even when English might use have just sent.

So أرسلتُ الرسالةَ للتوِّ naturally expresses a recently completed action. Arabic does not need a separate present perfect form the way English does.

للتوِّ is an idiomatic expression meaning just now, only a moment ago, or just in the sense of something that happened very recently.

It is very common in Modern Standard Arabic, especially in writing and formal speech.

It is best learned as a fixed expression: للتوِّ = just now.

You do not usually need to break it down when you are starting out. Native speakers understand it as one time expression.

الرسالة is definite, so it means a specific message or letter that is known from the context.

• الرسالة = the message / the letter
• رسالة = a message / a letter

Arabic often uses the definite form when both speaker and listener know which thing is being talked about.

It can mean either one.

رسالة can refer to:

• a written letter
• a message
• sometimes even a broader communication

The exact meaning depends on context. In modern everyday contexts, it is often understood as message, but letter is also perfectly possible.

Because الرسالة is the direct object of the verb أرسل.

The verb أرسل means to send, and the thing being sent comes directly after it:

• أرسلتُ الرسالةَ = I sent the message

If you want to mention the recipient, then you would add a preposition such as إلى:

• أرسلتُ الرسالةَ إلى المدير = I sent the message to the manager

In ordinary Arabic writing, short vowel endings are usually omitted, but grammatically they are still there.

In full form:

• أرسلتُ: verb with ـتُ for first person singular
• الرسالةَ: direct object, so it is in the accusative
• للتوِّ: after the preposition لـ, so it is in the genitive

That is why the fully vocalized sentence is أرسلتُ الرسالةَ للتوِّ.

Because ر is a sun letter.

When ال comes before a sun letter, the l sound of the article assimilates to the next consonant. So:

• الرسالة is pronounced ar-risāla

The same thing happens in للتوِّ, because ت is also a sun letter, so the pronunciation has a doubled t sound.

No, Arabic word order is flexible.

أرسلتُ الرسالةَ للتوِّ is a very natural neutral order: verb + object + time expression.

But other orders are possible for emphasis or style, such as:

• أنا أرسلتُ الرسالةَ للتوِّ for emphasis on I
• أرسلتُ للتوِّ الرسالةَ in a more marked style

The original sentence is the most straightforward standard way to say it.

No. أرسلتُ الرسالةَ للتوِّ is already complete and correct on its own.

You can add لقد for emphasis or a slightly more formal written tone:

لقد أرسلتُ الرسالةَ للتوِّ

That can make the completion of the action feel a bit more explicit, but it is optional.