Like the title says, I am able to receive email from external email accounts (hotmail etc.) but I cannot send anything to that same hotmail account or any other account.

I followed the admin UI guide here Sending mail through an external relay - Zimbra :: Wiki

I used smtp.google.com assuming that it doesnt require authentication and should work for me.. but it isnt. are there free smtp relay servers that i can use since that one seems to not be working for me.