Forward-Confirmed Reverse DNS (FCrDNS) is a non-negotiable requirement for direct outbound mail servers. If an ISP cannot resolve your IP address back to the exact domain name declared in your SMTP `HELO` command, your connection will be dropped at the TCP handshake stage.
1. Establishing Forward-Confirmed Reverse DNS
| Step | Record Type | Host / Target Alignment |
|---|---|---|
| 1. Forward A Record | A | mail.outreachdomain.com → 192.0.2.100 |
| 2. Reverse PTR Record | PTR | 100.2.0.192.in-addr.arpa → mail.outreachdomain.com |
| 3. SMTP HELO Banner | MTA Config | Must announce mail.outreachdomain.com during connection greeting. |
