DNS domain name not found sending email to postfix

Question

I'm in the process of setting up a postfix server on an EC2 instance to send / receive email.

I'm running into a series of problems, which I believe are mostly caused by incorrect DNS records.

I currently have my MX records setup with GoDaddy as follows

[A record, Host: mail, Points to: Elastic IP address]

[A record, Host: @, Points to: Elastic IP address]

[MX record, Priority: 10, Host: @, Points to: mail.mydomain.com]

Where my domain.com is the domain for which I'm editing the DNS zone file. This configuration is based on MX Records help - Godaddy DNS and Ubuntu Postfix email account with forward

However, when I send an email to [e-mail], I receive the following delivery error:

Technical details of temporary failure:

DNS Error: Domain name not found

I've setup a Unix user "test", but my guess is that the outbound mail isn't even resolving the mydomain.com domain name.

Any help debugging this DNS record issue would be appreciated.

Answer 1

I found out that the issue was not with the DNS records but with EC2 firewalls. Depending on the EC2 security group that you've placed your instance in, inbound / outbound traffic may be blocked on several of your ports (including 25, in my case).

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-network-security.html

I opened port 25 to inbound traffic under the AWS EC2 dashboard and was able to successfully send / receive mail.