There's not much that can be done about it other than formatting it manually or running some kind of macro over it.
A text file is just a file full of characters and word wrap is a feature of notepad. MS Word and others do this based on page size and margins, eg. if you copy text from Word to notepad (word wrap off) it will extend the lines across the page until it sees a line terminator character. See here for reference - Newline - Wikipedia, the free encyclopedia
If a text file is added to a e-mail as an attachment it can be saved to the computer and then opened by notepad. Also depending on the e-mail application used it may be displayed in the msg wrapped or not. I done a test using Thunderbird and it displayed my text file in the msg and automatically wrapped it based on my window size.
EDIT: I'm slow, two replies since I started this.