Separate HTTPs/HTTP Traffic from IMAP/POP3/SMTP Traffic with 2 ISPs

to add on you then goto Network > Policy Routes > Create New

You would then select following

protocol as TCP

Incoming interface : Your inside interface/s

Source address: internal subnet/s

Destination address: 0.0.0.0/0

Source Ports : leave them alone

Destination Ports :   from : 80 to 80

Select the outgoing interface and add the gateway.

You will have to create a few policies to get the final result as you cant add multiple ports. Also in the sources field you can configure the firewall to interpret the address you dont want to forward this way, kind of like a bypass list by going into the CLI and setting the following on that policy.

config router policy

edit <sequence number of policy>

set src-negate enable

next

end