diff -r a5e70c14214a -r 8919cc4f63b4 hgext/patchbomb.py
--- a/hgext/patchbomb.py	Mon Jul 16 18:17:19 2018 -0400
+++ b/hgext/patchbomb.py	Mon Jul 16 18:17:44 2018 -0400
@@ -818,6 +818,8 @@
             generator = emailgen.Generator(_bytesgenerator(fp),
                                            mangle_from_=False)
             generator.flatten(m, 0)
-            sendmail(sender_addr, to + bcc + cc, fp.getvalue())
+            alldests = to + bcc + cc
+            alldests = [encoding.strfromlocal(d) for d in alldests]
+            sendmail(sender_addr, alldests, fp.getvalue())
 
     progress.complete()