Lots of 'Returned mail' with error 550 "JunkMail rejected" from valid acct

Hi there. I'm hoping this is something that I can fix through WHM or cPanel but I'm not actually sure if that is the source of the issue.

The situation is that I have an ecommerce store on Network Solutions, they also host Email accounts associated with the domain I have there. We'll call the domain mystore.com, therefore I have an Email such as orders@mystore.com.
I then have my primary service with InMotionhosting which has the WHM/cPanel on it, this is where our primary domains/websites/email are hosted for our business. We don't actually use the Email accounts hosted on Network Solutions.
Because of that, I have setup the NS EMail to simply forward to three of our normal EMail accounts. So basically orders@mystore.com forwards to bob@, jill@, mary@. Make sense? Normally it only forwards to two accounts but since we've been having this issue I added myself as the third name so that I could receive some of these returned messages directly, and I have, like over 20 of them in the last week. Plus the other two Email accounts get returned messages too but it is random. For example I will get returned messages to my box saying that delivery failed to their boxes. Or they will get returned messages saying it failed to go to my box or each others.

OK, so down to the issue. Every returned message has the same subject line:
"Returned mail: see transcript for details"

I won't quote the entire Email to save space, but basically it sounds like NS is returning the mail because the "remote server" (i.e. my WHM server) "would not or could not accept the message". According to this Email, NS is saying they are not the cause of the problem, and they are just reporting what my server did. If I believe this, then the problem is really on my server.

Then down below in the message it says "The following addresses had permanent fatal errors" and lists one of the three addresses I forward to, all three on my WHM server. Sometimes it says it failed to deliver to jill@, sometimes bob@, etc. I even got one message saying it failed to deliver to MY address, even though the returned message was actually in my inbox to begin with! How can it fail to send to me when it actually sent the error to me to begin with? Strange. It's like telling someone over the phone that you are unable to call them on the phone. But anyway.
Here is the crux of the error, and this I will quote (personal data scrubbed):

I did not scrub the "myregisteredsite" address and IP, that is the actual Network Solutions mail server. I realize that the problem here is that my server seems to be thinking NS is a spammer, and is in the block list, and if I go to that spamcop link, it appears the IP is in the BL. However, it is hit and miss, sometimes spamcop does report the IP in the BL, but sometimes it doesn't and says the IP isn't listed.

Bottom line is this, I don't care if the NS IP got in a BL at some point, they send Email from many many IPs, some I found in BL, some not. The point is I just need to make sure all Email from Network Solutions is allowed so we can stop getting these friggin returned messages a dozen a day!

The only thing I tried is, in WHM, in the Exim config, under "Only-verify-recipient" I added the IP range "209.17.112.0/20". Unless I read incorrectly, this means Exim will trust mail coming from that IP range. This range seems to be where most NS mail is coming from. However, adding the IP to that Access List did nothing and we're still getting returned messages.

I hope all that makes sense. If I read it right, mail from NS is trying to forward to my three addresses, but randomly one of the addresses will be rejected by my server, saying the NS mail server is spam? However, since the bounce is coming FROM NS, they are reporting in the Email that they are NOT the problem, and just reporting what my server said. This is all very circular and I'm not sure where the actual source of the problem is.

I've attached an image with the full Email message in case it helps.

Thanks a bunch for any advice. If it IS my server, I'd just as soon white list NS and be done with it, I don't care if they have a random IP that got in a black list, I need my mail from my store!

 

Re: Lots of 'Returned mail' with error 550 "JunkMail rejected" from valid a

Any takers?

 

Re: Lots of 'Returned mail' with error 550 "JunkMail rejected" from valid a

Seriously, I'd like to know what this means.

If nothing else, just tell me how to prevent my server from blocking anything from Network Solutions.

Thanks.