How can I set the title of a UIButton as left-aligned?

Set the contentHorizontalAlignment:

// Swift 
emailBtn.contentHorizontalAlignment = .left;

// Objective-C
emailBtn.contentHorizontalAlignment = UIControlContentHorizontalAlignmentLeft;

You might also want to adjust the content left inset otherwise the text will touch the left border:

// Swift 3 and up:
emailBtn.contentEdgeInsets = UIEdgeInsets(top: 0, left: 10, bottom: 0, right: 0);

// Objective-C
emailBtn.contentEdgeInsets = UIEdgeInsetsMake(0, 10, 0, 0);