I configured a server (A) as a WireGuard server and SSH jumphost for two other servers (B and C). B and C accept SSH connections only from A’s public IP.
This works well in a split tunnel variant (with only the tunnel’s IP subnet, DNS IPs and the public IPs of A, B and C defined as AllowedIPs), as well as a full tunnel variant. SSH connections are fast and stable, and using the web (through the full tunnel) is also reasonably fast.
But when sending email to server B (which is my mail server), the connection takes forever on both cases (split and full tunnel). A’s firewall does not accept SMTP connections, but this should not matter because the connections goes through the tunnel; and B obviously accepts email connections from any IP. After approximately 30 seconds, emails are transferred successfully. What is going on here?
