How to send an email with Arduino and a WiFi shield?

You actually present 2 issues here, which can be handled separately: You are concerned about having a WiFi, not an Ethernet shield. This doesnt affect at all for sending emails or any other network stuff. When you have internet connection, it is almost transparent from the programming side. So I recommend first to try your wifi shield connection and configuration as a separate problem, with a more simple task, as a simple HTTP_GET to a known web page. A function like this might help, assuming that you have an instance of WiFiClient (which is a Client), that has been connected (with connect) to the URL and port 80: void http_get(Client& www, char website[], char webpage[], int timeout, Stream& stream) { if (www.connected()) { int n = www.print("GET "); www.print(webpage); www.print(" HTTP/1.1\r\n"); www.print("Host: "); www.print(website); www.print("\r\n"); www.print("\r\n"); } else { stream.println(F("Connection failed get")); return; } /* Read data until either the connection is closed, or the idle timeout is reached. */ unsigned long lastRead = millis(); while (www.connected() && (millis() - lastRead < timeout)) { while (www.available()) { char c = www.read(); stream.print(c); lastRead = millis(); } } } The second problem is that you want to send an email. One you have a connection, it doesnt matter if it is wifi or wired. The above recommended libraries (SMTPClient, FullIP) will directly connect to your provider (e.g. gmail) and will request your gmail password, something that is not secure over non secure connections (and those libraries do not seem to provide secure layer), so personally I am not comfortable with that option. I have been using the http://www.temboo.com service, that allows to send emails, and I have found it to be quite convenient and simple. Furthermore, they also have many other services. The service stores your gmail or whatever provider credentials, and you access the service via a Secret Key and App Password they provide. While this keys might not be fully secure to be sent via non secure layers, at least it only compromises your app in the cloud application, which you might simply manage, and not your full email account. (Disclaimer: I have no relation with temboo, and there might be other similar services for this task, e.g. https://www.carriots.com/documentation/arduino, I simply say that I have used them with success for this task and feel it is relatively simple). Your code using temboo, could be something like: TembooChoreo choreo(client); // your WiFiClient object // Set Temboo account credentials choreo.setAccountName(temboo_account); choreo.setAppKeyName(temboo_app); choreo.setAppKey(temboo_app_key); // credential is the name of your gmail profile in temboo choreo.setCredential(credential); choreo.addInput("MessageBody", body); choreo.addInput("Subject", subject); choreo.addInput("ToAddress", address); //Identify the Choreo to run choreo.setChoreo("/Library/Google/Gmail/SendEmail"); choreo.run(); choreo.close();

There may be a problem with sending Email from Arduino, but not where you are expecting it. SMTP protocol is super simple, even Arduino can handle it. But you will need SMTP server somewhere that will talk to your Arduino. SSL connections (as on Gmail) are out of consideration (code to handle the encryption would be too much for Arduino) so you'd have to find mail provider that provides plain SMTP - and there aren't many. If you will set up one yourself, say on your home PC with static IP address, it would be an invitation for spammers and a guaranteed way to get your IP blacklisted by Spamhaus. My advice would be to have Python, PHP or Perl script hosted somewhere that will handle HTTP POST requests from your Arduino and do Email sending. It is safer and simpler.