I'm not sure if the message has been sent successfully.
～かどうかわからない、と言いたいときは、I'm not sure if ...の構文を使いましょう。
I don't know if でも同じ意味ですが、ここでは確信が持てないというニュアンスの not sureのほうがいいでしょう。
if 節の中身は、「主語＋動詞」の語順です。
なので、the message（主語）has been sent（動詞）となります。
メッセージは送られる物なので、受動態にします。
確認してください、というのは送った相手方に対するものであれば、
Will you just check? でＯＫです。
さらに具体的に、Will you look into your inbox?（受信箱を見てもらえますか）と言うこともできますね。
＜ボキャブラリー＞
not sure = 確信が持てない
successfully = うまく
sent successfully = うまく送信された
I'm not sure if the email was delivered successfully.
If you are not sure that your email was delivered correctly, you can say:-
1. I'm not sure if you received my email.
2. I'm not sure if the email was delivered successfully.
"もし、あなたの送ったメールがきちんと相手に届いているか確かではない時に言う事が出来ます。
1.I'm not sure if you received my email.
2.I'm not sure if the email was delivered correctly."
My email may have got lost on the net somewhere as I was preoccupied when I sent it.
I may have pressed the wrong button when I sent that email.
I may have messed up sending that email
The above expressions are all possible. Usually an explanation as to why you think it may have been sent incorrectly would help clarity "......as I was preoccupied when I sent it."
Preoccupied = Busy with attending to, or thinking about, other things.
To mess up = To do something wrong or incorrectly so that the process or activity is damaged.
"I was going to ask her to marry me, but I messed up. I drank too much (alcohol) and she couldn't understand a word I was saying!"
上記の表現はすべて使えます。それが誤送だと思われる理由についての説明で、 "......as I was preoccupied when I sent it."で、明快に説明できるでしょう。
Preoccupied =他のものに出席したり、考えたりしで忙しい。
To mess up = プロセスや活動が損なわれるように何かを間違っているか間違って行うこと。
"I was going to ask her to marry me, but I messed up. I drank too much (alcohol) and she couldn't understand a word I was saying!"
"私は彼女に私と結婚するように頼むつもりだったけど、大失敗しちゃった。飲みすぎて彼女が私が言っていた言葉を理解できなかった！
Can you kindly check if you have received the email that I have sent and let me know.
I am not sure if the email was sent successfully, can you confirm if you have received it.
>Can you kindly check if you have received the email that I have sent and let me know.
This is asking the person to check if he/she have received the email that you have sent.
>I am not sure if the email was sent successfully, can you confirm if you have received it.
*confirm=establish the correctness
Can you kindly check if you have received the email that I have sent and let me know.
自分が送ったEメールを受け取ったかどうか確認したい時に尋ねる時の表現です。
I am not sure if the email was sent successfully, can you confirm if you have received it.
*confirm=正しいかどうかを確認するという意味です。
Something that is successful achieves what it was intended to achieve. Someone who is successful achieves what they intended to achieve.
'I'm not sure if the email was sent successfully'
How successful will this new treatment be?
I am looking forward to a long and successful partnership with him.
She has been comparatively successful in maintaining her privacy.
successful なものというと、するべきことができるもののことを言います。successful な人というと、活性したいことを達成した人のことを意味します。
'I'm not sure if the email was sent successfully.'
（そのメールが無事に送られたかどうかわからない。）
How successful will this new treatment be?
（この治療法はどれほど聞くだろうか？）
I am looking forward to a long and successful partnership with him.'
（彼との長く成功したパートナーシップを楽しみにしています。）
She has been comparatively successful in maintaining her privacy.
（彼女はプライバシーを守るのにいくらか成功している。）
I think the email you received may have being sent prematurally.
This sentence will allow you to express that fact the email may have some errors. Or it may be a way to accept that there are errors in the email and will need to resend the email.
We can use 'prematurely' to show when something happened before it was ready.
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