For some reason, I've always though italics was depicted like this in a MSS _This is Italics_ But recently, I have read a lot of threads on another forum and everyone says to underline the italics. I'm not sure how I came to learn/think that italics should be represented like _this_ What about when you send sample pages in an e-mail?
Standard manuscript format is to use underscoring to indicate italics. But that said, you should always consult the specific guidelines of wherever you're submitting to. Different publishers and agencies may have slight variations on the standard. I have seen italicised sections of a manuscript indicated with _, but I think it's fairly rare (and more for situations where underscoring isn't possible, such as in txt files). With sample pages in an email, I'm unsure. Honestly I don't think I've seen anywhere that has asked for submitted material in the body of an email rather than as an attachment.
A lot of places ask for query letters with 5-10 sample pages and absolutely no attachments at all. Sample chapters must be pasted in body of e-mail after the letter.
yes, many do now ask for material to be included in the body of the email... but that doesn't affect underscoring words you want to see printed in italics... and i can't imagine where you got the idea that it should be like _this_ unless that was instructions for writers who use a typewriter and are too lazy to go back and underscore after they've typed the words...