Use another SMTP server when sending emails to Yahoo address?

You could add a smarthost router. Add something like:

smarthost:
driver = manualroute
domains = yahoo.com
transport = remote_smtp
route_data = "other.server.net"

after the democheck router in your exim.conf.

The only downside is that you will have to check a valid mail account from this server on other.server.net so that this server will be able to relay mail through other.server.net. Or you will need to modify the exim configuration on other.server.net to always allow relaying from this server.

This then presents another problem, you then effectively have an open relay allowing this server to always send out mail through other.server.net. Probably not a huge deal since in order for someone to take advantage of this they would have to have an account on this server and if they already have an account on this server they could just use that server to send out mail.

 

other.server.net would be whatever server you are wanting to send out mail through.

Is the other server a cPanel server? That is the assumption that I was working on, but it doesn't have to be the case. The main IP address of your server needs to be able to relay mail through other.server.net. On a cPanel server this can be accomplished by writing a perl script or fetchmail or some other system to log into a valid POP account (it can be a dummy POP account) on other.server.net so that your server's main IP is always listed in the relayhosts file on other.server.net and can always relay mail through it. There may be alternative methods for accomplishing this same task.

If other.server.net is not a cPanel server, then it would depend on what type of relaying model that server provides. If you can configure other.server.net to always allow relaying from your server's main IP address then you wouldn't need the POP-before-SMTP aspect.

 

I wanted to follow up on your message since I'm dealing with a similar situation. After confirming with Barracuda and numerous spam lists and relay databases that none of the IPs in my subnet (255.255.255.248) are blacklisted, I finally learned that another server in the same Class C network was reported for spam.

Some mail providers will now arbitrarily block mail from entire Class C blocks if they detects spam or malware originating from one or more hosts on that network. Unfortunately, I have no control over hosts in other subnets on the same Class C, so a smarthost seems like the only feasible solution.