To forward traffic from one destination to another (such as from the public IP to an internal mail server), the dst-nat action is used in MikroTik NAT rules.
* dst-nat: Modifies the destination IP address and/or port of the packet. Used to forward traffic to an internal resource.
* tarpit: Captures and holds TCP connections (used for spam traps or slowing down bots) ##
* passthrough: Used in mangle rules; allows the packet to be evaluated by the next rule ##
* redirect: Redirects traffic to the router itself (e.g., proxy or DNS services) ## So, for external SMTP traffic (e.g., TCP port 25), we use a dst-nat rule that forwards the traffic to the internal mail server.
MTCNA NAT Section - Destination NAT:
"To forward SMTP traffic from a public address to a private server, use dst-nat with appropriate port and IP." Rene Meneses Guide - Practical NAT Examples:
"Use dst-nat for port forwarding. Redirect is for internal services like DNS or web proxy." Terry Combs Notes - NAT Action Summary:
"dst-nat = most common for external-to-internal mapping (e.g., mail servers, web servers)."