Changing MX record and DNS cache
Posted on 2016-10-02
Recently I have to configure new Spam filter on my Exchange server 2003.
The mx record looked like this before change;
xxx.com MX mail.xxx.com
mail.xxx.com A 18.104.22.168(my exchange server)
Now pointed mail.xxx.com to 333.333.333.333(spam filter)
333.333.333.333 will forward the filtered emails to my exchange server 22.214.171.124
From now, I will say 126.96.36.199 as 2 and 333.333.333.333 as 3.
After the change, about half of emails are sent directly to 2, not to 3, and most of them are spams.
I guess this is caused by the spam sender's DNS cache still has our MX and A records.
I thought if I change A record of mail.xxx.com from 2 to 3, the emails will be all redirected to 3, but as I inspected headers of spams, they are still sending emails directly to 2. How can I fix this problem? Should I change the MX record as well, like 'xxx.com MX mail2.xxx.com'? Is there anyway to propagate DNS record change immediately? TTL on both MX and A records are 3600 sec in Dyn.com. They said DNS cache will be cleared at most 24 hours, but it doesn't look like. I changed last Friday, still I'm getting lots of spams directly to my exchange server.