Actually if you are talking about mail server only (inbound connections), then the best way to have a failover - is to have 2 MX records for yuor domain (via primary and via secondary ISP), so you won't be dependant on DNS TTL.
So, nedd need for other tools, as SMTP has built-in feature.
I would also note that it's possible for mail server to accept inbound connection via both ISPs (simultaneously) if you could assign additinal internal IP-address to your mail server, or could assign additional port to SMTP listener.
Please let me know your scenario and I could help you to craft the config.
This document gives several answers on frequently asked questions for PFRv3 channel state behavior.
Q1: What are all the channel operational states from a BR (border role) perspective and what are the rules/conditions to be in each st...
The need was to reach an host inside a LAN through a VPN connection managed by the LAN gateway (Cisco 1921).
The LAN gateway performs NAT and there was a dedicate nat rule for the host i wanted to reach through VPN.
I couldn't connect to the hos...
We have 3 identical switches configured by someone else and would like to claim some of the Gigabit ports(G1/G2/G3/G4) for use on servers. When we try to change the wiring and configuration, we run in to connectivity issues. Attached is a des...