We have recently changed our ISP, I have changed the mail and mailserver DNS 'A' records for our domain name to point to the new external static IP address assigned to the router by the new ISP (the MX record points to mail.<mydomain> as always) but I am not getting any email (though sending email works). Do I just have to wait will the change is reflected in DNS caches? I am slightly concerned because I can connect to the web email service made visible through the new router which suggests that the mail.<mydomain> static I.P. address change has happened.
mxtoolbox.com reports an 'A' type DNS record pointing to the static IP address of the router, but clicking on smtp diag on that web page results in :
Timeout occurred due to inactivity.
Port 25 is not open on mail.<mydomain> (presumably blocked by the router) should it be?
Have I missed something?
Best Answer
Please don't use the word propagation when you should be using the words cache and/or caching. Using the word propagation in relation to DNS caching only serves to "propagate" the misunderstanding that DNS records propagate, which they don't.
When referring to DNS caching, it's only relevant to systems that have those particular records cached, which most certainly is not very many in this case. I would find it very hard to believe that you're not recieving ANY email due to DNS record caching.
At any rate, it looks like the problem is a firewall issue, based on the fact that your tests seem to be indicating that you can't telnet to port 25 of your email server from the outside. Since you just changed your ISP and were allocated different ip addresses, I would suggest looking at the NAT configuration of your firewall to make sure you've got the correct external ip address NAT'ed to the correct internal ip address.