You can state the report is being sent if it is on its way. Of course, if you claim it's been sent, you have to remember that it's still being sent, which means it hasn't arrived yet. Keep in mind that I did not transmit it. The word sent does not mean that I released the message into space or anything like that. Rather, it just means that I have placed the file onto an electronic mailing list for transmission at a later date.
A letter has been sent implies that the letter has been put in the post. If there has been some kind of mistake and the letter hasn't gone out, then people will ask if it has been sent correctly. This isn't too problematic because most people know what being sent means but sometimes it can be confusing for others. For example, if I say that my report has been sent and then realize I need to change something about it before I send it off again, I could say "I've sent it back to myself for adjustment".
Being told that a letter has been sent makes me wonder whether it has been delivered. If it hasn't, then someone will probably ask when they will get it.
It's been sent implies that the thing being sent has been separated from its original owner or provider.
The letter was received. The word "is" emphasizes the fact that you now have the letter. The word "has been" emphasizes the fact that you had the letter previously. I had a nasty letter before, but I don't have it now. It has been received.
The past tense and past participle of send is sent/sent/.
"It has been delivered" is a present perfect passive sentence, not a past continuous sentence. The phrase "it was delivered" places the act of delivery in the past. "It has been delivered" concentrates on the current ramifications of the previous delivery.
It would enough to say: the letter has already been sent to our office, or the letter was sent to our office yesterday. It should be noted that "has been" is normally used for a previous occurrence with no precise timeline, however "was" is preferable if the chronology is mentioned (i.e. yesterday).
In this case, since the letter will be delivered to our office today, we need to use "was sent".
Also note that if you are writing about multiple letters then it must be written "a letter and another one". Otherwise, it will be understood that you are talking about two different letters.
Sentences containing letters - there are many kinds of sentences where you can find letters in them. Let's see some examples: "The letter A is used to strike objects with." "Bread is often cut into squares instead of slices because letter E is used for cutting bread." "My favorite color is red because R is used to denote red, white, or black."
Let's write some sentences yourself. You can use letters to show who does what in a sentence. For example, let's say that my sister sends me a letter every year on my birthday. Here are some possible sentences: "My sister sends me a letter every year on my birthday." "I send her a card on her birthday." "She sends me a gift on her birthday."
Whether you say "an email has been sent" or "an email was sent" depends on what sounds better in context, in my opinion.