No, no, no, no, no! In spanish you look like a perfect idiot if you write an email in all caps!
And of course it is incorrect not to use accent marks in capital letters. The reasons sometimes they are not there are various: With at least some typewriters it was impossible to place the accent over a capital letter; It is, or was, easier (and cheaper, I am sure) to find fonts without them for some applications; They take up space, so if you want your store's sign to be as big as possible you will maybe do away with them...

Maybe you have seen a lot of posts written in spanish in all caps, I know I have, but spanish is not the magic language that you can understand better in caps. Whenever I have to read one it feels like some idiot shouting nonsense. Of course it does not help that more often than not these same posts do not offer the slightest clue to the reader in the form of punctuation or a basic respect for grammar. If that is what comes out of that "person"'s head, I am confident s/he is an idiot.

Please do not go around saying these things, I don't need more texts in all caps.