To configure a mail in your iPhone / iPad application, import the given class in your header file. And add a new framework called "MessageUI.framework" to your frameworks folder.

#import <MessageUI/MessageUI.h>
#import <MessageUI/MFMailComposeViewController.h>

We also need to create a label to show the message and button action to perform actions as showPicker, displayComposerSheet, launchMailAppOnDevice as given below..

    -(IBAction)showPicker:(id)sender
    {   
        Class mailClass = (NSClassFromString(@"MFMailComposeViewController"));
        if (mailClass != nil)
        {
            // We must always check whether the current device is configured for sending emails
            if ([mailClass canSendMail])
            {
                [self displayComposerSheet];
            }
            else
            {
                [self launchMailAppOnDevice];
            }
        }
        else
        {
            [self launchMailAppOnDevice];
        }
    }

    -(void)displayComposerSheet 
    {
        MFMailComposeViewController *picker = [[MFMailComposeViewController alloc] init];
        picker.mailComposeDelegate = self;

        [picker setSubject:@"Hello from California!"];


        // Set up recipients
        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"]; 

        [picker setToRecipients:toRecipients];
        [picker setCcRecipients:ccRecipients];  
        [picker setBccRecipients:bccRecipients];

        // Attach an image to the email
        NSString *path = [[NSBundle mainBundle] pathForResource:@"rainy" ofType:@"png"];
        NSData *myData = [NSData dataWithContentsOfFile:path];
        [picker addAttachmentData:myData mimeType:@"image/png" fileName:@"rainy"];

        // Fill out the email body text
        NSString *emailBody = @"It is raining in sunny California!";
        [picker setMessageBody:emailBody isHTML:NO];

        [self presentModalViewController:picker animated:YES];
        [picker release];
    }
// Dismisses the email composition interface when users tap Cancel or Send. Proceeds to update the message field with the result of the operation.
- (void)mailComposeController:(MFMailComposeViewController*)controller didFinishWithResult:(MFMailComposeResult)result error:(NSError*)error 
{   
    message.hidden = NO;
    // Notifies users about errors associated with the interface
    switch (result)
    {
        case MFMailComposeResultCancelled:
            message.text = @"Result: canceled";
            break;
        case MFMailComposeResultSaved:
            message.text = @"Result: saved";
            break;
        case MFMailComposeResultSent:
            message.text = @"Result: sent";
            break;
        case MFMailComposeResultFailed:
            message.text = @"Result: failed";
            break;
        default:
            message.text = @"Result: not sent";
            break;
    }
    [self dismissModalViewControllerAnimated:YES];
}

// Launches the Mail application on the device.
-(void)launchMailAppOnDevice
{
    NSString *recipients = @"mailto:first@example.com?cc=second@example.com,third@example.com&subject=Hello from California!";
    NSString *body = @"&body=It is raining in sunny California!";

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

    [[UIApplication sharedApplication] openURL:[NSURL URLWithString:email]];
}

You can find a running example in Apple website for developers too :-)