The following CA certificate is intended to sign certificates that make using STARTTLS for mail transport possible. No guarantees of secrecy or authenticity are given; if you need that, sign+encrypt end-to-end.
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 15 (0xf)
    Signature Algorithm: sha1WithRSAEncryption
        Issuer: C=US, ST=California, L=Palo Alto, O=NetBSD for TLS only, OU=Mail CA, CN=Postmaster NetBSD.org/emailAddress=postmaster@NetBSD.org
        Validity
            Not Before: Jul 23 10:38:56 2017 GMT
            Not After : Aug 31 10:38:56 2027 GMT
        Subject: C=US, ST=California, O=NetBSD for TLS only, CN=mail.NetBSD.org CA/emailAddress=postmaster@NetBSD.org
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (4096 bit)
                Modulus:
                    00:d2:50:c6:01:3b:37:e2:fc:97:02:61:db:fb:4c:
                    ab:c7:73:60:cc:f8:b1:3e:e5:1f:39:0d:8b:2b:2d:
                    83:74:9a:4e:60:55:22:48:64:72:d4:48:ef:65:b2:
                    cf:73:90:76:7e:3f:b3:cf:78:61:b8:ce:f7:d6:ef:
                    20:9b:d9:ae:41:66:d0:c9:21:b5:2c:bb:2d:dc:57:
                    63:75:86:75:0c:09:23:06:c4:d5:2d:55:49:f9:70:
                    3a:b5:3e:17:76:64:ac:e8:0d:06:92:78:7c:d6:57:
                    e4:62:b9:39:e7:0d:cf:70:7b:8e:bb:1c:cc:3a:1d:
                    66:10:58:9d:3b:95:24:a8:5d:ae:4d:64:ac:49:78:
                    f9:3f:a7:96:e0:f3:67:c1:6c:b2:c6:1a:44:ae:37:
                    5e:72:af:b8:df:5b:78:fc:19:09:aa:e9:01:ea:68:
                    93:7d:81:64:54:57:55:ea:82:35:45:07:f8:6b:d4:
                    8b:95:01:0e:4a:ee:3e:67:cf:7c:42:93:7f:d7:2f:
                    a1:e0:93:d2:45:82:e8:18:d6:30:a6:62:57:40:63:
                    44:34:92:d7:7b:b4:64:f7:a9:09:0b:21:92:35:55:
                    5e:8c:82:df:8e:31:fa:83:1c:7f:e3:86:ce:7f:f9:
                    c3:4e:7a:fc:58:6d:26:1d:0c:2d:96:e9:12:2c:7f:
                    d3:5c:f4:89:c3:62:54:e1:ab:e4:d7:71:8c:cd:fb:
                    cb:b7:4a:9b:ef:6b:cf:3e:e7:25:11:3a:a8:f0:04:
                    64:a1:55:79:ae:72:25:b2:db:9e:96:05:13:8e:7b:
                    98:d1:27:10:06:e2:f5:6c:30:a6:1d:7b:bf:fa:6c:
                    e8:8b:8f:6f:24:93:57:9e:c5:f0:26:25:2e:16:27:
                    5e:78:aa:1a:fc:ec:8a:65:9b:b2:e4:c2:38:24:cb:
                    b0:ee:6c:3a:55:d1:14:98:18:46:00:75:f0:1f:ed:
                    e7:5b:62:ce:63:2b:8b:78:eb:55:9b:28:e7:51:cb:
                    af:e4:35:a1:8f:60:25:a0:ea:b0:37:3b:18:9f:61:
                    6e:e5:be:0b:6a:3c:16:96:4e:6e:57:a2:71:54:5d:
                    f6:21:e1:28:65:78:cb:03:fa:6b:0f:56:bd:a2:d2:
                    66:57:78:e5:01:37:e3:ef:b2:81:e1:3f:1e:e1:c0:
                    b9:ac:f4:e0:ff:47:44:d0:31:77:fe:25:b5:97:22:
                    fe:c6:66:cb:99:d7:59:94:b2:5f:fd:fa:43:d7:3b:
                    09:6c:f9:9a:39:81:06:2b:f4:ed:8b:64:dc:de:36:
                    42:8d:8f:8c:39:fa:89:15:ae:62:d4:ac:e1:20:2b:
                    52:4d:75:e9:68:1a:61:92:48:9a:8f:e0:dd:d7:36:
                    62:b6:f3
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:TRUE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                85:E9:80:8C:A0:AE:19:62:75:3D:EF:DC:35:ED:A8:52:C2:E7:77:FC
            X509v3 Authority Key Identifier: 
                keyid:56:69:4E:2C:E7:F9:8D:EF:E7:20:2C:91:9A:34:CB:78:42:2D:19:2A
                DirName:/C=US/ST=California/L=Palo Alto/O=NetBSD for TLS only/OU=Mail CA/CN=Postmaster NetBSD.org/emailAddress=postmaster@NetBSD.org
                serial:00

    Signature Algorithm: sha1WithRSAEncryption
         03:f8:26:78:d7:6a:cb:a5:63:7f:0f:a1:d7:9a:e6:15:8b:89:
         dd:5f:20:b9:1b:4f:ab:6e:6e:4f:87:19:40:ba:9b:ce:22:a6:
         07:af:5c:79:a2:64:b2:35:30:96:dd:5c:94:00:66:09:bb:b1:
         29:b2:cc:5c:23:51:7b:2a:b4:41:1a:10:61:36:8e:8a:02:dc:
         ab:8b:00:b7:a2:06:ed:6f:90:4f:00:4b:e9:ef:df:1f:7b:a1:
         6f:67:19:db:d1:d8:c9:50:78:67:b5:be:47:8a:2c:1e:17:0e:
         f3:30:d6:05:08:13:8a:75:f1:49:28:5b:41:92:d7:7b:61:9e:
         e9:56
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----