A pretty rough example for sending an emil!

emailDemo.cpp

#define SMTP_SERVER "smtp.yourserver.com"
#define SMTP_USER_BASE64 "base64_encode_your_user"
#define SMTP_PASS_BASE64 "base64_encode_your_pass"

#define SMTP_FROM_EMAIL "email@from.com"
#define SMTP_TO_EMAIL "email@to.com"
#define SMTP_SUBJECT "Email from a Core!"
#define SMTP_BODY "Body body body"

#include "application.h"
#include <string.h>


//void idle();
//int SendEmail(char *smtpServer, char *username, char *password, char *fromEmail, char *toEmail, char *subject, char *body);
//int handshake(char *smtpServer);
//int authenticate(char *username, char *password);
//void echoSocketWrite(TCPClient src, const char *line) ;
//void echoSocketWrite(TCPClient src, String line);
//void flushToSerial(TCPClient src);
//int blockForResponse(char *response, unsigned int maxWait);


TCPClient client;
int sentOnce = 0;

void setup() {
    pinMode(D0, INPUT_PULLDOWN);
    Spark.variable("emailSent", &sentOnce, INT);
    
    Serial.begin(9600);
}



void loop() {
    if (digitalRead(D0) == HIGH) {
        if (sentOnce == 0) {
            RGB.control(true);
            
            RGB.color(250, 0,0);

            sentOnce = SendEmail(SMTP_SERVER, SMTP_USER_BASE64, SMTP_PASS_BASE64, SMTP_FROM_EMAIL, SMTP_TO_EMAIL, SMTP_SUBJECT, SMTP_BODY);
            
            if (sentOnce) {
	            RGB.color(0, 250, 0);
            }
            RGB.control(false);
        }
    }
}

void idle() {
    SPARK_WLAN_Loop();
}

/**
 * Thank you @jboswell !
 */
int SendEmail(char *smtpServer, char *username, char *password, char *fromEmail, char *toEmail, char *subject, char *body) {

    if (!client.connect(smtpServer, 25)) {
         return 0;
    }


    Serial.write("Connected!\n");
    
    if (!handshake(smtpServer)) {
        Serial.write("handshake failed...");
        client.stop();
        return 0;
    }
    
    if (!authenticate(username, password)) {
        Serial.write("auth failed...");
        client.stop();
        return 0;
    }
    
    
    Serial.write("sending mail...\n");
    echoSocketWrite(client, String("MAIL FROM:<") + String(fromEmail) + String(">") + String("\r\n"));
    echoSocketWrite(client, String("RCPT TO:<") + String(toEmail) + String(">") + String("\r\n"));
    flushToSerial(client); //client.flush();

    echoSocketWrite(client, "DATA\r\n");
    echoSocketWrite(client, String("from: ") + String(fromEmail) + String("\r\n"));
    echoSocketWrite(client, String("to: ") + String(toEmail) + String("\r\n"));
    echoSocketWrite(client, String("subject: ") + String(subject) + String("\r\n"));
    flushToSerial(client); //client.flush();

    echoSocketWrite(client, "\r\n");
    echoSocketWrite(client, body);
    echoSocketWrite(client, "\r\n");
    echoSocketWrite(client, ".");
    echoSocketWrite(client, "\r\n");
    echoSocketWrite(client, "\r\n");
    flushToSerial(client); //client.flush();

    if (blockForResponse("250", 2500) == 1) {
    	Serial.write("Email sent.\n");
    }

    echoSocketWrite(client, "quit\r\n");
    echoSocketWrite(client, "\r\n");
    if (blockForResponse("220", 2500) == 1) {
    	Serial.write("Said goodbye.\n");
    }
    
    flushToSerial(client); //client.flush();
    client.stop();
    delay(100);
}


int handshake(char *smtpServer) {
    //wait for the server to say something.
    
    flushToSerial(client); //client.flush();
    Serial.write("waiting for the server to say hello...\n");
    if (blockForResponse("220", 5000) == 0) {
    	//handshake failed.
    	return 0;
    }
    idle();

    Serial.write("Saying hello back.\n");
    echoSocketWrite(client, String("EHLO ") + String(smtpServer) + String("\r\n"));
    if (blockForResponse("250", 1250) == 0) {
    	//handshake failed.
    	return 0;
    }
    idle();
    
    return 1;
}


int authenticate(char *username, char *password) {
    Serial.write("logging in...\n");
    echoSocketWrite(client, "AUTH LOGIN\r\n");
    blockForResponse("334", 5000);

    echoSocketWrite(client, String(username) + String("\r\n"));
    blockForResponse("334", 5000);

    echoSocketWrite(client, String(password) + String("\r\n"));
    blockForResponse("235", 5000);
     
    idle();
    return 1;
}



void echoSocketWrite(TCPClient src, const char *line) {
    Serial.write(line);
    src.print(line);
}
void echoSocketWrite(TCPClient src, String line) {
	flushToSerial(src);
	delay(10);

    Serial.write(line.c_str());
    src.print(line.c_str());
}

void flushToSerial(TCPClient src) {
    while (src.available()) {
        Serial.write(src.read());
    }
}

/* really basic / error prone way of listening for and parsing results */
int blockForResponse(char *response, unsigned int maxWait) {
    unsigned int startTime = millis();
    int idx = 0;
    char buffer[16];
    
    while ((millis() - startTime) < maxWait) {
        
        while (client.available()) {
            buffer[idx] = client.read();
            Serial.write(buffer[idx]);
            
            idx++;
            if (idx > 16) { 
                idx = 0; 
            }
            
            if (strstr(buffer, response) != NULL) {
                Serial.write("heard response.\n");
                return 1;
            }
        }
        
        delay(100);
    }
    
    Serial.write("timed out.\n");
    return 0;
}

Using this code will no longer give me any serial printouts. This is making extremely hard to debug.