Exchange 2010 Failover on SBS2011

We have a physical Exchange 2010 (SBS2011) server with the following setup:

mail.domain.nl pointing to our main WAN IP
MX (PTR) Record that points mail.domain.nl to our main WAN IP

I would like to do:
mail2.domain.nl that points to main WAN IP of second internet connection
add mail2.domain.nl to our MX (PTR) Record with lower priority

Expectation:
What I would like to acchieve is that the email can be sent out when we have downtime on our main internet connection.

How should this be setup?
In EMC:

Code:

Organisational Configuration --> Hub Transport --> Tab: Remote Domains

add second line for same domain (domain.nl)
Then I will see after change

Code:

1) Name: domain.nl / Domain: mail.domain.com --> Already excisting
2) Name: domain.nl / Domain: mail2.domain.com --> to be added

Finally contact our ISP to add second IP to SMTP server and Add second IP with lower priority to MX (PTR) Record?

I have not done this kind of implementation before, therefore I would like to get some advice first.