iPhone API已经提供了系统写邮件界面的接口,使用MFMailComposeViewController，用来显示界面.  
项目中需要添加MessageUi.framework。头文件加入MFMailComposeViewControllerDelegate。#import <MessageUI/MessageUI.h>  
sendMailViewController.m文件的实现：  
- (void)viewDidLoad  
{  
    UIButton *button = [UIButton buttonWithType: UIButtonTypeRoundedRect];  
    button.frame = CGRectMake(0, 40, 320, 50);  
    [button setTitle: @"Mail" forState: UIControlStateNormal];  
    [button addTarget: self action: @selector(sendEMail) forControlEvents: UIControlEventTouchUpInside];  
    [self.view addSubview: button];  
}  

- (void) alertWithTitle: (NSString *)_title_ msg: (NSString *)msg   
{  
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:_title_   
                                                    message:msg   
                                                   delegate:nil   
                                          cancelButtonTitle:@"确定"   
                                          otherButtonTitles:nil];  
    [alert show];  
    [alert release];  
}   

//点击按钮后，触发这个方法  
-(void)sendEMail   
{  
    Class mailClass = (NSClassFromString(@"MFMailComposeViewController"));  

    if (mailClass != nil)  
    {  
        if ([mailClass canSendMail])  
        {  
            [self displayComposerSheet];  
        }   
        else   
        {  
            [self launchMailAppOnDevice];  
        }  
    }   
    else   
    {  
        [self launchMailAppOnDevice];  
    }      
}  
//可以发送邮件的话  
-(void)displayComposerSheet   
{  
    MFMailComposeViewController *mailPicker = [[MFMailComposeViewController alloc] init];  

    mailPicker.mailComposeDelegate = self;  

    //设置主题  
    [mailPicker setSubject: @"eMail主题"];  

    // 添加发送者  
    NSArray *toRecipients = [NSArray arrayWithObject: @"first@example.com"];  
    //NSArray *ccRecipients = [NSArray arrayWithObjects:@"second@example.com", @"third@example.com", nil];  
    //NSArray *bccRecipients = [NSArray arrayWithObject:@"fourth@example.com", nil];  
    [mailPicker setToRecipients: toRecipients];  
    //[picker setCcRecipients:ccRecipients];      
    //[picker setBccRecipients:bccRecipients];  

    // 添加图片  
    UIImage *addPic = [UIImage imageNamed: @"123.jpg"];  
    NSData *imageData = UIImagePNGRepresentation(addPic);            // png  
    // NSData *imageData = UIImageJPEGRepresentation(addPic, 1);    // jpeg  
    [mailPicker addAttachmentData: imageData mimeType: @"" fileName: @"123.jpg"];  

    NSString *emailBody = @"eMail 正文";  
    [mailPicker setMessageBody:emailBody isHTML:YES];  

    [self presentModalViewController: mailPicker animated:YES];  
    [mailPicker release];  
}  
-(void)launchMailAppOnDevice  
{  
    NSString *recipients = @"mailto:first@example.com&subject=my email!";  
    //@"mailto:first@example.com?cc=second@example.com,third@example.com&subject=my email!";  
    NSString *body = @"&body=email body!";  

    NSString *email = [NSString stringWithFormat:@"%@%@", recipients, body];  
    email = [email stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];  

    [[UIApplication sharedApplication] openURL: [NSURL URLWithString:email]];  
}  
- (void)mailComposeController:(MFMailComposeViewController *)controller   
          didFinishWithResult:(MFMailComposeResult)result error:(NSError *)error   
{  
    NSString *msg;  

    switch (result)   
    {  
        case MFMailComposeResultCancelled:  
            msg = @"邮件发送取消";  
            break;  
        case MFMailComposeResultSaved:  
            msg = @"邮件保存成功";  
            [self alertWithTitle:nil msg:msg];  
            break;  
        case MFMailComposeResultSent:  
            msg = @"邮件发送成功";  
            [self alertWithTitle:nil msg:msg];  
            break;  
        case MFMailComposeResultFailed:  
            msg = @"邮件发送失败";  
            [self alertWithTitle:nil msg:msg];  
            break;  
        default:  
            break;  
    }  

    [self dismissModalViewControllerAnimated:YES];  
}