MX Record propogation time - Email working sometimes and sometimes not

Question

I have tried to migrate my hosting from Hostgator to AWS yesterday. I have removed the DNS of HostGator and made it to the default of the service provider from whom i bought the domain and created A record to point to AWS public IP. After some time I realized it broke the MX record and I have reverted back the DNS settings to Hostgator itself. I'm using Gmail for business and the HostGator MX records point to Gmail.

I wasn't getting emails initially for 6 hours. and then It started working for few services like yahoo and gmail but the emails between the team itself wasn't working. All the email communications started working fine after sometime. Now again we are facing issues with the team emails. We are geting the email bounce reply.

Please let me know if i have missed something. Will the issue persist till the propagation time. My doubt is why it's working for sometime and again it starts failing. Its already around 18 hours since i updated the dns.

Answer 1

When changing DNS providers it is very important to be careful to duplicate the zone file between the providers and to keep it online at the old provider for at least 48-72 hours before terminating it to ensure globally all DNS queries are being sent to the new DNS provider. In your example what it sounds like is that when you added the A record for the AWS public IP to your zone file with your registrar you didn't add the relevant MX records. What you need to do is log into your HostGator control panel. open the DNS advanced editor which will show you every single entry in your zone file. What you then want to do is duplicate them all from the HostGator settings into your registrar's DNS control panel. In particular make sure that any TXT and MX records are duplicated precisely.

In order to make it easier rather than trying to identify which records to duplicate the best rule of thumb is to duplicate every single record except for the SOA record. The SOA record will be different on the new DNS server and should have been set up by your provider already but all the other records should be duplicated precisely. Once you have done that keep the old records on the HostGator account for at least 72 hours. Once that time has gone through all DNS queries should not be going through the new DNS server and you can shut down your old hosting account.