Python Code

from tkinter import *
import smtplib

class App(object):
    def __init__(self):
        self.window = Tk()
        self.window.wm_title("Messaging")

        self.label = Label(self.window, text="Email", font=("Sans",20))
        self.label.pack(padx=50,pady=20)

        self.label2 = Label(self.window, text="Recipient:")
        self.label2.pack()
        self.recipient = Entry(self.window")
        self.recipient.pack(pady=10)


        self.label3 = Label(self.window, text="Subject:")
        self.label3.pack()
        self.subject = Entry(self.window)
        self.subject.pack(pady=10)

        self.label4 = Label(self.window, text="Message:")
        self.label4.pack()
        self.message = Entry(self.window)
        self.message.pack(pady=10)

        self.send = Button(self.window, text="Send", command=self.sendEmail(self.recipient.get(),self.subject.get(),self.message.get()))
        self.send.pack(pady=20)

        self.window.mainloop()

    def sendEmail(self, rec, sub, msg):
        with open('pass.txt') as f:
            credentials = [x.strip().split(':') for x in f.readlines()]

        #setup username and password for authentication
        userName = ""
        userPass = ""

        for username,password in credentials:
            userName = username
            userPass = password

        if userName == rec:
            print("You cannot send emails to yourself.")
        else:
            self.smtpObj = smtplib.SMTP("smtp.gmail.com", 587)
            self.smtpObj.ehlo()
            self.smtpObj.starttls()
            self.smtpObj.login(userName,userPass)
            self.smtpObj.sendmail(userName,rec,("Subject: %s\n%s"%(sub,msg)))
            self.smtpObj.quit()

App()