Yes, you can delete, a message you sent but only if the person you sent it to has not opened it yet. You can also edit it, if you forgot something, made a mistake, want to correct something, etc.

If you are not already in the email section then go to My Profile scroll down to My Email and click. From there you will be at your My Email page and your Inbox will be open. On it's menu bar is Outbox this is the sent mail folder.

Once you click on Outbox you will go to the mail you sent. You will notice that next to the profile picture is a little envelope icon. If the email has been read it's triangular "flap" will be up, or open, and this means the person you sent it to has read it. If it is not opened and looks rectangular then the mail has not been read.

On the right hand side of window is a set of three envelope icons. The bottom one has a red "x" on it. Click this to delete the email.

Deleted emails can't be read on SGS by the originally-intended recipient but if the person you wrote to has "email notification" set up to send a message to their internet email address they will still be able to read your message even if you have deleted it, so let what you write always reflect good judgment.