I would like to change the following script so that it only sends an email if a particular skype contact has logged in. How is it done?

(File name: skype_logged_in.sh)
#!/bin/bash
ssmtp a.com < ./skype_notifications/skype_logged_in.txt (this contains email content)

The above is called from the script line in the generic "Contact came Online" notification in skype. I have put the following into the skype script box:

sh skype_logged_in.sh

Robin