Assuming that you actually get here to this part, here's some reasons that military emails are fake, aside from the fact that they are ALWAYS a scam.
If you have read about how to identify a scam email (which is here) then in addition to things like bad grammar, poor spelling, even poorer punctuation, the use of free email servers, etc. these are some other things that make a "military" scam format completely bogus.
What's the scam?
The military scam format is a form of the so-called "Advanced fee fraud". You would keep paying money for a bunch of fake documents and so on that will cost you money but you will never get that money. The soldier will say the money has been transfered, fees are needed for transportation, safekeeping in a warehouse, customs releases etc.
1. I am am American solider.
No they are not. They are never American soldiers. Real American soldiers do not behave this way.
2. I am in Iraq.
No they aren't. You're dealing with a scammer criminal and Iraq is probably the last place he is located. He is more likely to be close to if not exactly in Nigeria. They almost always are.
3. I found some money in Iraq.
Cool. Even if they did, you can't keep this kind of thing secret in the military. Everyone will know and everyone will talk. You cannot hide money.
4. This is completely legal.
So is being arrested and imprisoned at Ft. Leavenworth, Kansas, which is the main U.S. military prison. Every single member of the military knows that if they tried something like moving stolen money around like this they would end up here, for many, many years. This is explained to them on day 1 in the military.
5. "...I am in the Engineering Unit of US Military here in [name of place]....
No they aren't. The unit they mention may or may not be currently deployed in Iraq. In any case you got an email from a scammer.
6. "I am an American soldier in Iraq/Afghanistan"...but my email was sent to you from Nigeria.
Yeah, so what's the deal with that? Scam mail? Yes, delete it and forget it.
7. "I have in my possession the sum of USD 11.5 million, which I got from crude oil deals in Iraq".
American military personnel are NOT allowed to trade in any commodities while they are in uniform and in service in another country. It's illegal. Likewise, probably every other military service in the world, at least the better run operations, are not permitted to trade in commodities while in uniform. You have an email from a scammer/criminal so just delete it.