Sending an email from swift 3

It will not work with simulator. Please test it on iPhone device. You can refer Apple Developer Portal - MFMailComposeViewController

Sending an Email is quit easy in Swift 5 you need to confirm and implement MFMailComposeViewControllerDelegate and check if we can send email on this device

Here is the tiny piece of code I was using for my task

import UIKit
import MessageUI

class ViewController: UIViewController, MFMailComposeViewControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    //MARK: IBAction Method for Button click
    @IBAction func sendEmail(_ sender: Any) {
        //TODO:  You should chack if we can send email or not
        if MFMailComposeViewController.canSendMail() {
            let mail = MFMailComposeViewController()
            mail.mailComposeDelegate = self
            mail.setToRecipients(["[email protected]"])
            mail.setSubject("Email Subject Here")
            mail.setMessageBody("<p>You're so awesome!</p>", isHTML: true)
            present(mail, animated: true)
        } else {
            print("Application is not able to send an email")
        }
    }

    //MARK: MFMail Compose ViewController Delegate method
    func mailComposeController(_ controller: MFMailComposeViewController, didFinishWith result: MFMailComposeResult, error: Error?) {
        controller.dismiss(animated: true)
    }
}

PS: Please don't forget you need to test this on real device

Here's how I did it. It looks like you followed the documentation very well, I thought I'd add my variation in case it helps someone else. Plus, this is a little more updated to current (Aug 2017) syntax.

Conform to the MFMailComposeViewControllerDelegate protocol, and check if the device can send mail.

import Foundation
import UIKit
import MessageUI

class WelcomeViewController: UIViewController, MFMailComposeViewControllerDelegate {


override func viewDidLoad() {
    super.viewDidLoad()

    if !MFMailComposeViewController.canSendMail() {
        print("Mail services are not available")
        return
    }
}

My app uses an IBAction to initiate the mail composition.

@IBAction func sendFeedbackButtonTapped(_ sender: Any) {

    let composeVC = MFMailComposeViewController()
    composeVC.mailComposeDelegate = self

    // Configure the fields of the interface.
    composeVC.setToRecipients(["[email protected]"])
    composeVC.setSubject("Message Subject")
    composeVC.setMessageBody("Message content.", isHTML: false)

    // Present the view controller modally.
    self.present(composeVC, animated: true, completion: nil)

}

About the following mailComposeController function, the documentation says

The mail compose view controller is not dismissed automatically. When the user taps the buttons to send the email or cancel the interface, the mail compose view controller calls the mailComposeController(_:didFinishWith:error:) method of its delegate. Your implementation of that method must dismiss the view controller explicitly, as shown in Listing 3. You can also use this method to check the result of the operation.

func mailComposeController(_ controller: MFMailComposeViewController,
                           didFinishWith result: MFMailComposeResult, error: Error?) {
    // Check the result or perform other tasks.

    // Dismiss the mail compose view controller.
    controller.dismiss(animated: true, completion: nil)
   }
}

Source Apple Documentation: MFMailComposeViewController