Sysadmin reading server local emails

sounds like your server doesn't have properly working IPv6 networking ?

what do you get for ipv6 ping of the google smtp server ?

Code (Text):

ping6 -c4 alt2.gmail-smtp-in.l.google.com

i.e.

Code (Text):

ping6 -c4 alt2.gmail-smtp-in.l.google.com

PING alt2.gmail-smtp-in.l.google.com(sb-in-x1b.1e100.net (2404:6800:4003:c01::1b)) 56 data bytes
64 bytes from sb-in-x1b.1e100.net (2404:6800:4003:c01::1b): icmp_seq=1 ttl=37 time=296 ms
64 bytes from sb-in-x1b.1e100.net (2404:6800:4003:c01::1b): icmp_seq=2 ttl=37 time=296 ms
64 bytes from sb-in-x1b.1e100.net (2404:6800:4003:c01::1b): icmp_seq=3 ttl=37 time=296 ms
64 bytes from sb-in-x1b.1e100.net (2404:6800:4003:c01::1b): icmp_seq=4 ttl=37 time=296 ms

--- alt2.gmail-smtp-in.l.google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 296.773/296.882/296.933/0.390 ms

and openssl smtp check

Code (Text):

echo | openssl s_client -connect alt2.gmail-smtp-in.l.google.com:25 -starttls smtp

i.e.

Code (Text):

echo | openssl s_client -connect alt2.gmail-smtp-in.l.google.com:25 -starttls smtp   
CONNECTED(00000003)
depth=2 C = US, O = GeoTrust Inc., CN = GeoTrust Global CA
verify return:1
depth=1 C = US, O = Google Inc, CN = Google Internet Authority G2
verify return:1
depth=0 C = US, ST = California, L = Mountain View, O = Google Inc, CN = mx.google.com
verify return:1
---
Certificate chain
 0 s:/C=US/ST=California/L=Mountain View/O=Google Inc/CN=mx.google.com
   i:/C=US/O=Google Inc/CN=Google Internet Authority G2
 1 s:/C=US/O=Google Inc/CN=Google Internet Authority G2
   i:/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
 2 s:/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
   i:/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
---
Server certificate
-----BEGIN CERTIFICATE-----
M....SNIPPED....IP
-----END CERTIFICATE-----
subject=/C=US/ST=California/L=Mountain View/O=Google Inc/CN=mx.google.com
issuer=/C=US/O=Google Inc/CN=Google Internet Authority G2
---
No client certificate CA names sent
Peer signing digest: SHA256
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 4636 bytes and written 450 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
    Session-ID: 4AED981F610B886C4425E0E8873DA2F732F390C2FAEA1F5D7BB1893043D5D865
    Session-ID-ctx: 
    Master-Key: C7513422F05A01847D2F2CC9FE94C81872078F376D2E5AB4EA1A65B3CBDF1F0AB6050D455BF663AD4608B947B17AACC3
    Key-Arg   : None
    Krb5 Principal: None
    PSK identity: None
    PSK identity hint: None
    TLS session ticket lifetime hint: 100799 (seconds)
    TLS session ticket:
    0000 - 00 fb 7d 91 28 bc 98 2f-a1 4e ae 3b 77 25 43 70   ..}.(../.N.;w%Cp
    0010 - 7c e5 70 b4 55 7d 91 ca-9e bd d7 be 54 6e 21 53   |.p.U}......Tn!S
    0020 - fb f2 e3 f4 18 19 24 e1-e0 71 dd f8 04 60 a4 50   ......$..q...`.P
    0030 - ad 67 1b 56 0b a1 39 07-1e 14 aa a5 fd 5c 4c 3f   .g.V..9......\L?
    0040 - 1f 32 87 12 f9 f2 69 4b-d3 6f f8 f7 7a af 88 3c   .2....iK.o..z..<
    0050 - 37 a6 a7 5d 2b c7 1e 51-9d b1 21 76 55 65 d0 53   7..]+..Q..!vUe.S
    0060 - 3b 20 39 4c 6d 5c 72 66-9b f1 d8 6f 95 b1 09 f1   ; 9Lm\rf...o....
    0070 - cb 75 93 12 1f eb 46 86-e9 dc 2c 96 d7 47 09 9b   .u....F...,..G..
    0080 - f6 96 bd 28 ac b8 93 e2-d4 04 e3 56 ec d6 60 68   ...(.......V..`h
    0090 - e6 f2 82 75 87 3d 48 c7-2e 60 9e d7 c9 45 50 8f   ...u.=H..`...EP.
    00a0 - 06 e1 31 99 a4 55 c7 c0-9a f2 a3 c5 a3 1e ff 38   ..1..U.........8
    00b0 - 0f c8 b4 76 66 de 0a f4-d3 47 4d ec ea 5b 89 cb   ...vf....GM..[..
    00c0 - b7 1f 4b 6f 51 e9 71 8b-c7 ba 5c 93 d6 0b bd bf   ..KoQ.q...\.....
    00d0 - b4 15 3e 99 f6                                    ..>..

    Start Time: 1509344950
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---
250 SMTPUTF8
DONE

 

Also you can direct root user emails to your email see Getting Started Guide step 18 for Managing root user emails

 

Centmin Mod installed CSF Firewall already opens port 25 but yes if you have a cloud based firewall in front, you will need to open it there too on Google Cloud

see Centmin Mod LEMP stack CSF Firewall default port listing

 

Postfix is already configured on Centmin Mod so do not need to setup/configure postfix just open port 25