Symptoms

1. SMTP email forwarding is set up from an address like support@company.tld -> support@support.company.tld, where company.tld is an email server (e.g., Gmail, VK, Yandex, or local), and support.company.tld is Swarmica.
2. Emails do not reach the ticket.
3. If you check the email box support@company.tld, the emails are there.
4. The sender's mail has bounces:
   Delivery Status Notification (Delay)
   454 4.7.1 : Relay access denied
5. The postfix logs on the server show errors like:
   Oct 02 19:04:42 support postfix/smtpd[147]: NOQUEUE: reject: RCPT from unknown[79.137.243.76]: 454 4.7.1 <support@support.swarmica.com>: Relay access denied; from=<msudyin@swarmica.com> to=<support@support.swarmica.com> proto=ESMTP helo=<fallback20.i.mail.ru>

Solution

Add the IP addresses of the email provider (for example, Gmail IP addresses) to the SMTP_NETWORKS variable and restart postfix:

vim .env
grep SMTP_NETWORKS .env
SMTP_NETWORKS=35.190.247.0/24,64.233.160.0/19,66.102.0.0/20,66.249.80.0/20,72.14.192.0/18,74.125.0.0/16,108.177.8.0/21,173.194.0.0/16,209.85.128.0/17,216.58.192.0/19,216.239.32.0/19,2001:4860:4000::/36,2404:6800:4000::/36,2607:f8b0:4000::/36,2800:3f0:4000::/36,2a00:1450:4000::/36,2c0f:fb50:4000::/36,172.217.0.0/19,172.217.32.0/20,172.217.128.0/19,172.217.160.0/20,172.217.192.0/19,172.253.56.0/21,172.253.112.0/20,108.177.96.0/19,35.191.0.0/16,130.211.0.0/22
docker-compose up -d

WARNING! THIS COMMAND WILL RESTART ALL APPLICATIONS - THERE WILL BE DOWN TIME

Cause

Incoming mail is handled by postfix, which by default does not allow connections from external IP addresses

For other providers

This error can also occur for other providers. For example, for VK Workspace, you need to set up SMTP_NETWORKS like this:

79.137.243.0/24,94.100.180.215/32,94.100.180.216/32,217.69.139.215/32,217.69.139.216/32

In general, you need to look at the SPF record of the domain from which the redirection is set up and add these servers