The comments below worked for me about changing the files. Here is what is said, I am also going to add a couple things for people who do not know to much about changing or navigating to the .lua folder.
Find the world of warcraft file. You can search it or under program files. Then go to interface then addons. Find EasyMail click on it and get into were the lua files are
Open up the EasyMail.lua with notepad
Press control and F at the same time and it will bring up a search box. Put playsound in it and hit find next.
search for "playsound" and for each instance replace
"igMainMenuOptionCheckBoxOn" with "856"
"UChatScrollButton" with "1115"
"igSpellBookOpen" with "829"
"igQuestFailed" with "847"
save and exit