You can't send email direct to Yahoo or Gmail at this time so you have to send it to smtp2go.com and they forward it on . Fortunately you do not have to give them your passwords for yahoo or gmail so your security is maintained.
You have to set up a free account at smtp2go.com
This program is put directly onto the ESP8266 chip using the Arduino IDE to upload the code. EmailsmtpESR8266.tar.gz……. http://www.esp8266.com/download/file.php?id=1136