在ios3.0及以后的版本中，你应该使用MFMailComposeViewController类，以及隐藏在MessageUI框架中的MFMailComposeViewControllerDelegate协议。

首先添加框架并导入:

#import <MessageUI/MFMailComposeViewController.h>

然后，发送一个消息:

MFMailComposeViewController* controller = [[MFMailComposeViewController alloc] init];
controller.mailComposeDelegate = self;
[controller setSubject:@"My Subject"];
[controller setMessageBody:@"Hello there." isHTML:NO]; 
if (controller) [self presentModalViewController:controller animated:YES];
[controller release];

然后用户完成工作，你及时得到委托回调:

- (void)mailComposeController:(MFMailComposeViewController*)controller  
          didFinishWithResult:(MFMailComposeResult)result 
                        error:(NSError*)error;
{
  if (result == MFMailComposeResultSent) {
    NSLog(@"It's away!");
  }
  [self dismissModalViewControllerAnimated:YES];
}

记得检查设备是否配置为发送电子邮件:

if ([MFMailComposeViewController canSendMail]) {
  // Show the composer
} else {
  // Handle the error
}

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。

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。

以下是Swift版本:

import MessageUI

class YourVC: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        if MFMailComposeViewController.canSendMail() {
            var emailTitle = "Vea Software Feedback"
            var messageBody = "Vea Software! :) "
            var toRecipents = ["pj@veasoftware.com"]
            var mc:MFMailComposeViewController = MFMailComposeViewController()
            mc.mailComposeDelegate = self
            mc.setSubject(emailTitle)
            mc.setMessageBody(messageBody, isHTML: false)
            mc.setToRecipients(toRecipents)
            self.presentViewController(mc, animated: true, completion: nil)
        } else {
            println("No email account found")
        }
    }
}

extension YourVC: MFMailComposeViewControllerDelegate {
    func mailComposeController(controller: MFMailComposeViewController!, didFinishWithResult result: MFMailComposeResult, error: NSError!) {
        switch result.value {
        case MFMailComposeResultCancelled.value:
            println("Mail Cancelled")
        case MFMailComposeResultSaved.value:
            println("Mail Saved")
        case MFMailComposeResultSent.value:
            println("Mail Sent")
        case MFMailComposeResultFailed.value:
            println("Mail Failed")
        default:
            break
        }
        self.dismissViewControllerAnimated(false, completion: nil)
    }
}

源

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;
}
}

下面的代码在我的应用程序中用于发送带有附件的电子邮件这里的附件是一张图片，你可以发送任何类型的文件唯一需要记住的是你必须指定正确的mimeType

将此添加到.h文件中

#import <MessageUI/MFMailComposeViewController.h>

将MessageUI.framework添加到项目文件中

NSArray *paths = SSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *getImagePath = [documentsDirectory stringByAppendingPathComponent:@"myGreenCard.png"];



MFMailComposeViewController* controller = [[MFMailComposeViewController alloc] init];
controller.mailComposeDelegate = self;
[controller setSubject:@"Green card application"];
[controller setMessageBody:@"Hi , <br/>  This is my new latest designed green card." isHTML:YES]; 
[controller addAttachmentData:[NSData dataWithContentsOfFile:getImagePath] mimeType:@"png" fileName:@"My Green Card"];
if (controller)
    [self presentModalViewController:controller animated:YES];
[controller release];

委托方法如下所示

  -(void)mailComposeController:(MFMailComposeViewController*)controller didFinishWithResult:(MFMailComposeResult)result error:(NSError*)error;
{
    if (result == MFMailComposeResultSent) {
        NSLog(@"It's away!");
    }
    [self dismissModalViewControllerAnimated:YES];
}