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 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 or NAT instance is missing from the Real-time Blackhole List and/or DNS Blacklist. For this, you can use specialized services, such as MX toolbox.

2. If the address is in the black 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 being compromised.

After resolving the issues that led to blacklisting, you may request the RBL/DNSBL list providers to delist your IP address.

If the issue persistsIf the issue persists

If the address is not on RBL/DNSBL lists, or the actions listed above did not help you solve the issue, create a support ticket. Provide the following information in your ticket:

1. ID of the problematic IP address (or the IP address itself).
2. Results of the IP address check using specialized tools or RBL provider interfaces.