Mail forwarded by routers does not use IP pools

[pplulee]

Describe the bug

Forwarded emails received by routes do not use IP pools to send messages.

To Reproduce

1. Enable and configure IP pools
2. Add a route with an address endpoint
3. Send an email to the address, the forwarded email is sending by system's default IP address

Screenshots

[willpower232]

I'm going to file this as a bug, mostly because I don't know enough about IP Pools, hopefully someone will be able to investigate and confirm where things are getting confused.