This kind of question is very good because it puts us on the spot in exactly the same way we often find ourselves in real life. Unfortunately, just like many questions on this site, we need to know a bit more about the context:
Is it someone you deal with on a daily basis? If so then you will use the "politeness level" you use with them all the time - probably neutral Japanese.
If they are asking you if you saw their mail then your response will follow the level and words they used in the question, so the conversation will be something like:
And you will wait for the next question, ready to give your view or explain the action taken.
If you are broaching the subject then:
1)You will ask them if they are busy.
2) If you have a view or a response that might take time then you introduce the subject first, giving them the opportunity to postpone the conversation.
3) At all times you have to be clear what you are talking about so as not to waste their time.
(This might all sound obvious but you have not described the scenario and although we are often concerned not to offend by using the wrong level of politeness, getting these things right may be more important to the superior)
So, having got their attention you will probably say something like:
And then, depending on the scenario be ready to follow up requested information/opinion etc.
Regarding level of politeness:
- If you want to say this to a very important person you do not often deal with and need to show reserve then the humble verb will be 拝見しました.
- くださる is used to refer to the other person's actions done for you.
- Humble forms such as お読みしました are used to describe actions you are doing for the other person to help them which may not apply to things have to as part of your job anyway!