Resolving issues with sending emails via SMTP from external IP addresses

Issue descriptionIssue description

• Recipients are not receiving emails sent from a mail server deployed on Yandex Cloud.
  As a mail server, you use a VM instance with an external IP address, or SMTP traffic is routed via a NAT instance.

SolutionSolution

1. Check whether your external IP address assigned to either the VM instance or NAT instance, is missing from the Real-time Blackhole List and/or DNS Blacklist. For this, you can use specialized services, for instance, MX toolbox.

2. If the address is present on the block list, verify the configuration of your mail server.
   The most common reasons for adding an IP address to RBL/DNSBL are:

   • Mass distribution of emails, which were marked as spam by their recipients.
   • No PTR and DMARC records for the external IP address.
   • Mail server compromise.
     After resolving issues that led to blacklisting, you may request the RBL/DNSBL list operators to delist your IP address.

3. If the address is not on RBL/DNSBL lists, or the actions listed above did not help solve the issue, create a request for technical support.

When creating the request, provide the following information:

• ID of the problematic IP address (or the IP address itself).
• Results of the IP address check using specialized services and/or RBL provider interfaces.