New servers, email problems

Hi Guys, Firstly, I have looked through the forums and searched about this issue but I think our setup is a bit more unique and I can't find any exact match solutions. We've moved over to a great new data centre near our main office, its not huge but the setup is really impressive with lots of Barracuda hardware for security etc etc. We have had WHM/cpanel servers for 10+ years and I wouldn't use anything else, but we've always had each server set up with its own 2 nameservers, both IP's consecutive, same subnets etc, so not *technically* set up correctly. We were keen to make proper use of having multiple nameservers, so we are running 3 whm servers in a DNS cluster, and the nameservers of every website we host are ns1.domain.ext ns1.domain.ext and the one main DNS server sorts it all out. Both NS are on different IPs on different subnets. We've also gone from dedi's to high spec virtual servers. There have been a few problems since moving, we'd been with the same provider for a long time so these guys didn't set things up quite the same - we were pretty much getting somewhere until a few days ago when suddenly web forms and email forwarders seemed to stop working. Originally I thought it was something to do with addon/parked domains and email forwarders that used them but it turns out its some (maybe most, its too early to know) web forms are not emailing out any more, and certain domains that we host, the email forwarders are no longer sending emails out. EG's; 1 [LIST]

Wordpress site with gravity forms hosted on whm server.

Form filled out

Form sends admin notification of form entry - it never arrives. (Admin email is google apps, email wasnt in spam)

Form sends out customer autoresponder - it does arrive (tested this with gmail) 2 [LIST]

User has email forwarder from whm server/cpanel to his gmail

User has gmail/google apps set to send as that forwarding address

User can email out as that user no probs as that just goes straight from gmail

Reply is not routed back to gmail/google apps so user never sees it Some email forwarders set up on one of the servers that point to another account on the servers also just don't work, internally or externally. I have recently set up a new email forwarder on one of the accounts that is having issues (as I i said, it could be all of them, too early to know) and sent a test email to it; 2015-11-18 20:32:41 1Zz9PF-0008BL-0V H=mail-lf0-f53.google.com [209.85.215.53]:3 6808 Warning: Message has been scanned: no virus or other harmful content was found 2015-11-18 20:32:41 1Zz9PF-0008BL-0V <= me@MyEmail.co.uk H=mail-lf0-f53.google .com [209.85.215.53]:36808 P=esmtps X=TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128 CV =no S=8137 id=CA+0=x70JAw=c-1ZFT62TOnLNstCECiRbp1HdQ5MEO_RpMs3_pQ@mail.gmail.com T="Testing!" for Order-Confirmed@domainname.co.uk 2015-11-18 20:32:41 1Zz9PF-0008BL-0V => useracc (Correct@forwardingAddress.com, Order-Confirmed@domainname.co.uk) R=local user T=local_delivery 2015-11-18 20:32:41 1Zz9PF-0008BL-0V Completed But the test email never appeared in his inbox. I just sent a test email from a form on a site hosted on one of the servers, this is the exmin log entry; 2015-11-18 20:46:20 1Zz9cS-000518-DO <= accountname@host.name.co.uk U=accountnameP=local S=3698 id=c23908452d1c70a95dd88a2bc803eee6@dijitul.uk T="Enquiry: 2741337" for correct@address.co.uk 2015-11-18 20:46:20 1Zz9cS-000518-DO => accountname2 R=localuser T=local_delivery 2015-11-18 20:46:20 1Zz9cS-000518-DO Completed correct@address.co.uk is a gmail group/forwarder that works if someone external emails it. Ive been moving websites over for a few months now ensuring things go smoothly and this happens at the last hurdle... Im sorry if my post is a bit waffly but I wanted to get as much info across as I could. Please ask for any more info that may help or suggest anything it could be. Many many thanks in advance.