问MFMailComposeViewController canSendMail返回是，但不在iOS中发送邮件

EN

MFMailComposeViewController *picker = [[MFMailComposeViewController alloc] init];
picker.mailComposeDelegate = self;

// Set the subject of email
[picker setSubject:@"My data file"];

// Add email addresses

[picker setToRecipients:[NSArray arrayWithObjects:emailId, nil]];


// Fill out the email body text
NSString *emailBody = @"Hello, \n Please find the data from the iOS app in the attachments.\n\n Thank you.\nMy Team.";

// This is not an HTML formatted email
[picker setMessageBody:emailBody isHTML:NO];

// Create NSData object from file
NSData *exportFileData = [NSData dataWithContentsOfFile:filePath];

// Attach image data to the email
[picker addAttachmentData:exportFileData mimeType:@"text/csv" fileName:  [self.CSVNameTextField text]];


// Show email view

if ([MFMailComposeViewController canSendMail]) {

    [self presentModalViewController:picker animated:YES];
}