diff -r 72b1715e18c1 -r 732e7d4515c0 Lib/email/base64mime.py
--- a/Lib/email/base64mime.py	Tue Apr 15 23:44:10 2014 -0400
+++ b/Lib/email/base64mime.py	Thu Apr 17 10:37:06 2014 -0400
@@ -35,7 +35,7 @@
     'header_encode',
     ]
 
-
+from base64 import urlsafe_b64decode
 from binascii import b2a_base64, a2b_base64
 from email.utils import fix_eols
 
@@ -172,7 +172,9 @@
     if not s:
         return s
 
-    dec = a2b_base64(s)
+    # Doing urlsafe b64decode is a little non-obvious, but a few email products
+    # seem to generate it. See #12489
+    dec = urlsafe_b64decode(s)
     if convert_eols:
         return dec.replace(CRLF, convert_eols)
     return dec
diff -r 72b1715e18c1 -r 732e7d4515c0 Lib/email/header.py
--- a/Lib/email/header.py	Tue Apr 15 23:44:10 2014 -0400
+++ b/Lib/email/header.py	Thu Apr 17 10:37:06 2014 -0400
@@ -101,7 +101,7 @@
                         encoded += '==='[:4 - paderr]
                     try:
                         dec = email.base64mime.decode(encoded)
-                    except binascii.Error:
+                    except TypeError:
                         # Turn this into a higher level exception.  BAW: Right
                         # now we throw the lower level exception away but
                         # when/if we get exception chaining, we'll preserve it.
diff -r 72b1715e18c1 -r 732e7d4515c0 Lib/email/test/test_email.py
--- a/Lib/email/test/test_email.py	Tue Apr 15 23:44:10 2014 -0400
+++ b/Lib/email/test/test_email.py	Thu Apr 17 10:37:06 2014 -0400
@@ -2773,6 +2773,9 @@
         eq(base64MIME.decode('aGVsbG8='), 'hello')
         eq(base64MIME.decode('aGVsbG8=', 'X'), 'hello')
         eq(base64MIME.decode('aGVsbG8NCndvcmxk\n', 'X'), 'helloXworld')
+        eq(base64MIME.decode(
+           'QW5tZWxkdW5nIE5ldHphbnNjaGx1c3MgU_xkcmluZzNwLmpwZw=='),
+           'Anmeldung Netzanschluss S\xfcdring3p.jpg')
 
     def test_encode(self):
         eq = self.assertEqual