IOS How to open mail application

These URLs launch Mail and open the compose message controller: 

NSString *stringURL = @"mailto:test@example.com";
NSURL *url = [NSURL URLWithString:stringURL];
[[UIApplication sharedApplication] openURL:url];

You can also provide more information, for a customized subject and body texts: 

NSString *subject = @"Message subject";
NSString *body = @"Message body";
NSString *address = @"test1@akosma.com";
NSString *cc = @"test2@akosma.com";
NSString *path = [NSString stringWithFormat:@"mailto:%@?cc=%@&subject=%@&body=%@", address, cc, subject, body];
NSURL *url = [NSURL URLWithString:[path stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
[[UIApplication sharedApplication] openURL:url]; 

You might also omit some information: 

NSString *subject = @"Message subject";
NSString *path = [NSString stringWithFormat:@"mailto:?subject=%@", subject];
NSURL *url = [NSURL URLWithString:[path stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
[[UIApplication sharedApplication] openURL:url];