Open eMail from App with predefined text in iOS

You can do it using MFMailComposeViewController:

import MessageUI

let mailComposerVC = MFMailComposeViewController()
mailComposerVC.mailComposeDelegate = self
mailComposerVC.setToRecipients(["[email protected]"])
mailComposerVC.setSubject("Subject")
mailComposerVC.setMessageBody("Body", isHTML: false)
self.presentViewController(mailComposerVC, animated: true, completion: nil)

Also, you need to implement mailComposeController:didFinishWithResult:error: from MFMailComposeViewControllerDelegate where you should dismiss MFMailComposeViewController

Swift 4.0

    let email = "[email protected]"
    let subject = "subject"
    let bodyText = "Please provide information that will help us to serve you better"
    if MFMailComposeViewController.canSendMail() {
        let mailComposerVC = MFMailComposeViewController()
        mailComposerVC.mailComposeDelegate = self
        mailComposerVC.setToRecipients([email])
        mailComposerVC.setSubject(subject)
        mailComposerVC.setMessageBody(bodyText, isHTML: true)
        self.present(mailComposerVC, animated: true, completion: nil)
    } else {
        let coded = "mailto:\(email)?subject=\(subject)&body=\(bodyText)".addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)
        if let emailURL = URL(string: coded!)
        {
            if UIApplication.shared.canOpenURL(emailURL)
            {
                UIApplication.shared.open(emailURL, options: [:], completionHandler: { (result) in
                    if !result {
                        // show some Toast or error alert
                        //("Your device is not currently configured to send mail.")
                    }
                })
            }
        }
    }

If you'd like to open the built-in email app as opposed to showing the MFMailComposeViewController as has been mentioned by others, you could construct a mailto: link like this:

let subject = "My subject"
let body = "The awesome body of my email."
let encodedParams = "subject=\(subject)&body=\(body)".stringByAddingPercentEncodingWithAllowedCharacters(.URLQueryAllowedCharacterSet())
let url = "mailto:[email protected]?\(encodedParams)"

if let emailURL = NSURL(url) {
    if UIApplication.sharedApplication().canOpenURL(emailURL) {
        UIApplication.sharedApplication().openURL(emailURL)
    }
}

---

Just to save anyone typing, for 2016 the syntax has changed slightly:

let subject = "Some subject"
let body = "Plenty of email body."
let coded = "mailto:[email protected]?subject=\(subject)&body=\(body)".stringByAddingPercentEncodingWithAllowedCharacters(.URLQueryAllowedCharacterSet())

if let emailURL:NSURL = NSURL(string: coded!)
    {
    if UIApplication.sharedApplication().canOpenURL(emailURL)
        {
        UIApplication.sharedApplication().openURL(emailURL)
        }

Swift 3 Version

let subject = "Some subject"
let body = "Plenty of email body."
let coded = "mailto:[email protected]?subject=\(subject)&body=\(body)".addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)

if let emailURL: NSURL = NSURL(string: coded!) {
    if UIApplication.shared.canOpenURL(emailURL as URL) {
        UIApplication.shared.openURL(emailURL as URL)
    }
}