Index: twisted/mail/test/server.pem
===================================================================
--- twisted/mail/test/server.pem	(revision 0)
+++ twisted/mail/test/server.pem	(revision 0)
@@ -0,0 +1,36 @@
+-----BEGIN CERTIFICATE-----
+MIIDBjCCAm+gAwIBAgIBATANBgkqhkiG9w0BAQQFADB7MQswCQYDVQQGEwJTRzER
+MA8GA1UEChMITTJDcnlwdG8xFDASBgNVBAsTC00yQ3J5cHRvIENBMSQwIgYDVQQD
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+WUQ9Ho4EzbYCOQ==
+-----END CERTIFICATE-----
+-----BEGIN RSA PRIVATE KEY-----
+MIIBPAIBAAJBAKy+e3dulvXzV7zoTZWc5TzgApr8DmeQHTYC8ydfzH7EECe4R1Xh
+5kwIzOuuFfn178FBiS84gngaNcrFi0Z5fAkCAwEAAQJBAIqm/bz4NA1H++Vx5Ewx
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+oolb6NMg/R3enNPvS1O4UU1H8wpaF77L4yiSWlE0p4w=
+-----END RSA PRIVATE KEY-----
+-----BEGIN CERTIFICATE REQUEST-----
+MIIBDTCBuAIBADBTMQswCQYDVQQGEwJTRzERMA8GA1UEChMITTJDcnlwdG8xEjAQ
+BgNVBAMTCWxvY2FsaG9zdDEdMBsGCSqGSIb3DQEJARYObmdwc0Bwb3N0MS5jb20w
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+Vq4BG021fJ9nlHRtr4rotpgHDX1rr+iWeHKsx4+5DRSy
+-----END CERTIFICATE REQUEST-----
Index: twisted/mail/tap.py
===================================================================
--- twisted/mail/tap.py	(revision 34342)
+++ twisted/mail/tap.py	(working copy)
@@ -17,6 +17,7 @@
 from twisted.mail import alias
 
 from twisted.mail.protocols import SSLContextFactory
+from twisted.internet.ssl import DefaultOpenSSLContextFactory
 
 from twisted.internet import endpoints
 
@@ -286,7 +287,8 @@
         category=DeprecationWarning, stacklevel=3)
 
     if certificate:
-        ctx = SSLContextFactory(certificate)
+        #ctx = SSLContextFactory(certificate)
+        ctx = DefaultOpenSSLContextFactory("server.pem", "server.pem")
         return endpoints.SSL4ServerEndpoint(reactor, port, ctx)
     return endpoints.TCP4ServerEndpoint(reactor, port)