title: Why do I get an Apple Mach-O Linker (ID) Error?
body: <p>I know that this question had been asked many times, but every answer seems different. I have built my project and tried to run it, but I get this error:</p>
  <pre><code>Ld &quot;/Users/******/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator/Cypher Bot.app/Cypher Bot&quot; normal i386
  cd &quot;/Users/******/Xcode/iOS/Cypher Bot/Universal/Cypher Bot/Cypher Bot&quot;
  setenv MACOSX_DEPLOYMENT_TARGET 10.6
  setenv PATH &quot;/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin&quot;
  /Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/clang -arch i386 -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.0.sdk -L/Users/********/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator -F/Users/**********/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator -filelist &quot;/Users/*******/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Intermediates/Cypher Bot.build/Debug-iphonesimulator/Cypher Bot.build/Objects-normal/i386/Cypher Bot.LinkFileList&quot; -mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -fobjc-arc -Xlinker -no_implicit_dylibs -D__IPHONE_OS_VERSION_MIN_REQUIRED=50000 -framework Security -framework UIKit -framework Foundation -framework CoreGraphics -framework CoreData -o &quot;/Users/********/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator/Cypher Bot.app/Cypher Bot&quot;
  
  Undefined symbols for architecture i386:
    &quot;_OBJC_CLASS_$_MFMailComposeViewController&quot;, referenced from:
    objc-class-ref in CryptoMainViewController.o
  ld: symbol(s) not found for architecture i386
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  <p>I also get this right below the message above:</p>
  <p><img src="https://i.stack.imgur.com/LqvL1.png" alt="Error" /></p>
  <p>What does this mean? What do I do to fix it?</p>