If you want your email to the agent to appear without any odd, unreadable symbols, you should be submitting your query letter and pages as plain text within the email. Yes, this means that the italicized words will appear as plain text. I had the same issue with my novel when I was querying.
What I did was, if the agent offered the option of querying by snail mail I did that (not the cheapest option, I know).
If the agent doesn't accept queries by snail mail you can email plain text and if you have an isolated word in a sentence that's italicized, you could mark it as italicized like _this_.
For an entire block of text that's italicized you're probably best to set this off on its own (double-space above and below so it's in its own paragraph).
Hope this helps.