The problem we wish to resolve is failed Reverse SMTP banner lookups.
- Publicly we have one IP with a single host name and MX record: 18.104.22.168 mail.domain.com
- Internally we have 6 servers that send out that same one public IP address
- All our internal servers have the default SMTP sending banner, which means they display "server#.internaldomain.lan" to the external recipient domain.
And so the questions/solutions:
- Can we set the FQDN in the SMTP sending gateway for all servers to be the same mail.domain.com and continue just using the one IP? Will this open other issues/problems?
- Or must we set each server to use a unique public IP, and set their respective FQDN. eg serv1/ip1, serv2/ip2 serv3/ip3...?
- Or must we setup a dedicated mail gateway(smarthost) with the proper SMTP banner.?