我写了一个简单的包装器KRNSendEmail，它简化了发送电子邮件到一个方法调用。 KRNSendEmail被很好地记录并添加到CocoaPods中。 https://github.com/ulian-onua/KRNSendEmail

如果你想从你的应用程序发送电子邮件，上面的代码是唯一的方法，除非你在你的应用程序内编写自己的邮件客户端(SMTP)，或者有一个服务器为你发送邮件。

例如，你可以编写你的应用程序来调用服务器上的URL，它会为你发送邮件。然后只需从代码中调用URL。

请注意，使用上面的代码，您不能向电子邮件附加任何内容，而SMTP客户端方法和服务器端方法允许您这样做。

MFMailComposeViewController是iPhone OS 3.0软件发布后的一种方式。您可以查看示例代码或我编写的教程。

斯威夫特2.2。改编自Esq的回答

import Foundation
import MessageUI

class MailSender: NSObject, MFMailComposeViewControllerDelegate {

    let parentVC: UIViewController

    init(parentVC: UIViewController) {
        self.parentVC = parentVC
        super.init()
    }

    func send(title: String, messageBody: String, toRecipients: [String]) {
        if MFMailComposeViewController.canSendMail() {
            let mc: MFMailComposeViewController = MFMailComposeViewController()
            mc.mailComposeDelegate = self
            mc.setSubject(title)
            mc.setMessageBody(messageBody, isHTML: false)
            mc.setToRecipients(toRecipients)
            parentVC.presentViewController(mc, animated: true, completion: nil)
        } else {
            print("No email account found.")
        }
    }

    func mailComposeController(controller: MFMailComposeViewController,
        didFinishWithResult result: MFMailComposeResult, error: NSError?) {

            switch result.rawValue {
            case MFMailComposeResultCancelled.rawValue: print("Mail Cancelled")
            case MFMailComposeResultSaved.rawValue: print("Mail Saved")
            case MFMailComposeResultSent.rawValue: print("Mail Sent")
            case MFMailComposeResultFailed.rawValue: print("Mail Failed")
            default: break
            }

            parentVC.dismissViewControllerAnimated(false, completion: nil)
    }
}

客户端代码:

var ms: MailSender?

@IBAction func onSendPressed(sender: AnyObject) {
    ms = MailSender(parentVC: self)
    let title = "Title"
    let messageBody = "https://stackoverflow.com/questions/310946/how-can-i-send-mail-from-an-iphone-application this question."
    let toRecipents = ["foo@bar.com"]
    ms?.send(title, messageBody: messageBody, toRecipents: toRecipents)
}

从iPhone应用程序发送电子邮件，你需要做下面的任务列表。

步骤1:导入# Import <MessageUI/MessageUI.h>在你想要发送电子邮件的控制器类中。

步骤2:添加委托到您的控制器如下所示

 @interface <yourControllerName> : UIViewController <MFMessageComposeViewControllerDelegate, MFMailComposeViewControllerDelegate>

步骤3:添加以下发送电子邮件的方法。

 - (void) sendEmail {
 // Check if your app support the email.
 if ([MFMailComposeViewController canSendMail]) {
    // Create an object of mail composer.
    MFMailComposeViewController *mailComposer =      [[MFMailComposeViewController alloc] init];
    // Add delegate to your self.
    mailComposer.mailComposeDelegate = self;
    // Add recipients to mail if you do not want to add default recipient then remove below line.
    [mailComposer setToRecipients:@[<add here your recipient objects>]];
    // Write email subject.
    [mailComposer setSubject:@“<Your Subject Here>”];
    // Set your email body and if body contains HTML then Pass “YES” in isHTML.
    [mailComposer setMessageBody:@“<Your Message Body>” isHTML:NO];
    // Show your mail composer.
    [self presentViewController:mailComposer animated:YES completion:NULL];
 }
 else {
 // Here you can show toast to user about not support to sending email.
}
}

步骤4:实现MFMailComposeViewController Delegate

- (void)mailComposeController:(MFMailComposeViewController *)controller didFinishWithResult:(MFMailComposeResult)result error:(nullable NSError *)error {
[controller dismissViewControllerAnimated:TRUE completion:nil];


switch (result) {
   case MFMailComposeResultSaved: {
    // Add code on save mail to draft.
    break;
}
case MFMailComposeResultSent: {
    // Add code on sent a mail.
    break;
}
case MFMailComposeResultCancelled: {
    // Add code on cancel a mail.
    break;
}
case MFMailComposeResultFailed: {
    // Add code on failed to send a mail.
    break;
}
default:
    break;
}
}

这里我想补充几点:

使用mailto URL在模拟器中不能作为邮件工作。应用程序未安装在模拟器上。但它在设备上确实有效。 mailto URL的长度有限制。如果URL大于4096个字符，请发送邮件。应用程序无法启动。 OS 3.0中有一个新类，可以让你在不离开应用程序的情况下发送电子邮件。请看类MFMailComposeViewController。