Some of our clients are experiencing delivery issues to some domains that use Gmail/Google for their email.

I previously covered that here – http://www.computersolutions.cn/blog/2015/04/gmail-and-other-google-hosted-mail-delivery-issues/

The issue is that China is still blocking Gmail/ Google hosted mail, and the recipient domain hasn’t setup their MX records correctly.

This is fine for servers outside of China, where all of googles mail servers (should) work, but breaks things for those inside China, where only a few servers are reachable.

Google hosted mail settings are here: https://support.google.com/a/answer/33915?hl=en

You’ll note that there are 5 different email servers that are listed in priority order.

Priority Mail Server
1 ASPMX.L.GOOGLE.COM.
5 ALT1.ASPMX.L.GOOGLE.COM.
5 ALT2.ASPMX.L.GOOGLE.COM.
10 ALT3.ASPMX.L.GOOGLE.COM.
10 ALT4.ASPMX.L.GOOGLE.COM.

For mail servers, the higher number is more important, so a priority of 1 will be the first server tried, then the next highest number, and so on.

If I try to connect to the servers from China.

telnet ASPMX.L.GOOGLE.COM 25
Trying 74.125.200.27…
(times out)

telnet ALT1.ASPMX.L.GOOGLE.COM 25
Trying 173.194.72.26…
(times out)

telnet ALT2.ASPMX.L.GOOGLE.COM 25
Trying 74.125.25.26…
(times out)

telnet ALT3.ASPMX.L.GOOGLE.COM 25
Trying 64.233.169.26…
Connected to ALT3.ASPMX.L.GOOGLE.COM.
Escape character is ‘^]’.
(yay, we have a winner!)

telnet ALT4.ASPMX.L.GOOGLE.COM 25
Trying 74.125.70.27…
Connected to ALT4.ASPMX.L.GOOGLE.COM.
Escape character is ‘^]’.
(yay, we have a winner!)

So, we can see that alt3, alt4 work, but none of the others do (as of 9th September 2015 from Shanghai)

So, some rudimentary testing shows that some servers work, and some do not.
How does that apply to real world examples.

Lets look at a non-working domain – ihg.com

dig mx ihg.com

;; ANSWER SECTION:
ihg.com. 600 IN MX 100 aspmx3.googlemail.com.
ihg.com. 600 IN MX 50 alt1.aspmx.l.google.com.
ihg.com. 600 IN MX 50 alt2.aspmx.l.google.com.
ihg.com. 600 IN MX 100 aspmx2.googlemail.com.
ihg.com. 600 IN MX 10 aspmx.l.google.com.

You should easily be able to see 2 things.
1 – that the MX records are not as per Google settings.
2 – that the 2 working MX records are not listed.

This means that while their MX records probably work oversea’s, they will not be deliverable from China. They need to amend their MX records to Googles recommended settings.

Lets look at another example.

dig mx rsms-west.com

;; ANSWER SECTION:
rsms-west.com. 6238 IN MX 30 alt2.aspmx.l.google.com.
rsms-west.com. 6238 IN MX 10 aspmx.l.google.com.
rsms-west.com. 6238 IN MX 40 aspmx2.googlemail.com.
rsms-west.com. 6238 IN MX 50 aspmx3.googlemail.com.
rsms-west.com. 6238 IN MX 20 alt1.aspmx.l.google.com.

Once again, we can see that the alt3, and alt4 servers are missing, and unfortunately none of the other listed servers are connectable from China.

Lastly, lets look at a working server

dig mx teamsequel.com

teamsequel.com. 12878 IN MX 1 ASPMX.L.GOOGLE.com.
teamsequel.com. 12878 IN MX 5 ALT1.ASPMX.L.GOOGLE.com.
teamsequel.com. 12878 IN MX 5 ALT2.ASPMX.L.GOOGLE.com.
teamsequel.com. 12878 IN MX 10 ALT3.ASPMX.L.GOOGLE.com.
teamsequel.com. 12878 IN MX 10 ALT4.ASPMX.L.GOOGLE.com.

You can see that they have the correct Gmail settings as per Gmail / Google settings page, and mail to them is deliverable (as alt3, alt4 are currently not being blocked by the beneficent government of China).

Unfortunately as this is an issue that is out of our control (MX records are incorrect, and China is being difficult), we cannot mitigate against it. The affected domains will need to amend their MX records appropriately as per the page here- https://support.google.com/a/answer/33915?hl=en.

When DNS goes bad

This year someone in China misconfigured something which effectively exported China’s main method of implementing blocks (man in the middle DNS spoofing) semi globally over the Global Crossing backbone for the last few weeks.

Effectively, China’s blocking, went global (for certain providers).

Read more »