Gmail doesn't allow SMTP connections via IPv6

[phunehehe0]

https://phunehehe.net/gmail-smtp-ipv6/

[p1mrx]

Your ISP is probably blocking SMTP-related ports inconsistently. Here's what I see from Comcast Residential:

  $ nmap -6 -Pn 2404:6800:4003:c02::6c
  
  Starting Nmap 7.10 ( https://nmap.org ) at 2016-03-27 17:38 PDT
  Nmap scan report for sc-in-x6c.1e100.net (2404:6800:4003:c02::6c)
  Host is up (0.18s latency).
  Not shown: 996 filtered ports
  PORT    STATE SERVICE
  465/tcp open  smtps
  587/tcp open  submission
  993/tcp open  imaps
  995/tcp open  pop3s
  
  Nmap done: 1 IP address (1 host up) scanned in 13.51 seconds
  
  $ nmap -Pn 74.125.68.108
  
  Starting Nmap 7.10 ( https://nmap.org ) at 2016-03-27 17:38 PDT
  Nmap scan report for sc-in-f108.1e100.net (74.125.68.108)
  Host is up (0.19s latency).
  Not shown: 996 filtered ports
  PORT    STATE SERVICE
  465/tcp open  smtps
  587/tcp open  submission
  993/tcp open  imaps
  995/tcp open  pop3s
  
  Nmap done: 1 IP address (1 host up) scanned in 12.86 seconds

[phunehehe0 → p1mrx]

I don't like the idea that Digital Ocean can be doing something that weird :) But it seems like you are right. I'll drop them a note.

    $ mtr --report-wide 2404:6800:4003:c02::6c --tcp --port 993
    Start: Mon Mar 28 03:23:08 2016
    HOST: phunehehe-do3                      Loss%   Snt   Last   Avg  Best  Wrst StDev
      1.|-- 2400:6180:0:d0:ffff:ffff:ffff:fff1  0.0%    10    0.7   1.1   0.3   6.5   1.9
      2.|-- 2400:6180::601                      0.0%    10    0.3   0.3   0.3   0.4   0.0
      3.|-- 2400:6180::301                      0.0%    10    0.9   0.6   0.3   1.3   0.0
      4.|-- 2001:4860:1:1:2:82d::               0.0%    10    0.9   1.8   0.9   3.8   0.7
      5.|-- 2001:4860::1:0:518d                 0.0%    10    1.7   2.0   1.7   2.2   0.0
      6.|-- 2001:4860::2:0:ab29                 0.0%    10    2.2   9.5   1.8  64.4  19.6
      7.|-- 2001:4860::2:0:ab28                40.0%    10    2.7   2.4   1.7   3.3   0.4
      8.|-- sc-in-x6c.1e100.net                70.0%    10  127.0 151.6 126.9 200.8  42.6

    $ mtr --report-wide 2404:6800:4003:c02::6c --tcp --port 465
    Start: Mon Mar 28 03:23:30 2016
    HOST: phunehehe-do3 Loss%   Snt   Last   Avg  Best  Wrst StDev

[p1mrx → phunehehe0]

Sounds like this, then:

https://warrenguy.me/blog/ipv6-digital-ocean-crippled

[phunehehe0 → p1mrx]

You are exactly right. Thanks again.