Outgoing email rules

I'm wondering if there's a rule for outgoing email. my comcast email is blacklisted when sending or responding to an email from the domain eastex.net. when i use my iCloud server... everything is ok. only emails to eastex.net are blocked when using the comcast domain. this affects only mail sent to eastex.net. all other outgoing email works just fine!

can i set up a rule... when i send email to the eastex.net domain... only my iCloud server is used. currently i go through three steps to make it work. thanks for any advice. if you have an answer... pls send step by step directions so i can follow. thanks again.