Try this syntax:
or you can do it this way....
echo -e "first line of mail" >> mymail.txt
echo -e "second line of mail" >> mymail.txt
cat mymail.txt | mail -s "test" firstname.lastname@example.org
This is the way I have found to work best... I think it just sits there because it is looking for the mail data, you would have to type it in followed by a "." which is the end message symbol. But I know for sure that the ways above work and that you do not need the "." and I hope this helps.