Is mail from x10hosting blocked?

[#1]

I've been using x10hosting for free storage of my web site for a few months, with a web redirect in place from my UK domain registrar to the x10hosting server and a separate redirect for email at the same domain via my Plusnet account.  Everything worked fine, except that because I hadn't transferred the hosting the URL appearing to users of my web site always showed an x10hosting domain.
I finally changed the web site hosting over to x10hosting yesterday and configured their email forwarding to point to my Plusnet account as before.  All email to me@mydomain now seems to get discarded, with no message back to the sender (within 12 hours anyway).  I tried the same redirect via a separate Yahoo account and it works fine.
I have a second domain (with no dedicated web site) and email redirected to my Plusnet account, and this still works fine.
Is Plusnet discarding email with x10hosting in the header automatically?  Or is there something else I should know about?
TIA,
David.

[#2]

To clarify ... Both my domains are registered with Fasthosts. I have just moved the hosting for the one with its own web site over to x10hosting and left the other with Fasthosts. It seems that mail for me at the latter domain gets through to my Plusnet account but for the former doesn't. Any suggestions welcome - or is my workaround using a non-Plusnet email account the only solution?
Thanks!
David

[#3]

Hi David,
It would help if you could set up the redirect that's not working but point it to a non-Plusnet email address. If you can then provide the full headers of an email received to the 3rd party address and raise a ticket containing them and an explanation regarding what's happening (feel free to link to this thread) then we can take it from there. Would also be handy to know whether or not x10hosting carry out any spam filtering prior to the mail being forwarded.

[#4]

Hi Bob,
Many thanks - I've raised a ticket referring to this thread and included the complete header from a successful test message redirected through Yahoo.
I guess that x10hosting doesn't do any spam filtering with outgoing mail (or at least it doesn't affect my test messages), since the same message redirected to a third party (Yahoo) account gets straight through in a few seconds.
To help with testing I've set up two directs (my domain name is in the mail header attached to the ticket):
info@... redirects to Plusnet
david@... redirects to Yahoo
I've just checked my webmail again (I use Thunderbird as a client that checks both my Plusnet and Yahoo accounts but doesn't download emails marked as spam) - a couple of my test messages have now come through to the Junk folder 24 hours later, although there are others that still haven't arrived.  So it looks like a spam filtering issue.
Kind regards,
David.

[#5]

Thanks David. This is the problem:

198.91.80.251 	CSI is currently publishing the reputation of this IP address as poor

The IP address of the mail server doing the forwarding for x10hosting has a poor reputation and our anti-spam appliances don't like it. I've passed your support ticket to our Operations Team to see if they can do anything about this.

[#6]

Thanks, Bob.
For now I've set up a separate 'disposable' Yahoo account and am forwarding email to my domain through that, but would prefer to use Plusnet eventually as its spam filtering is (you guessed it!) somewhat better 
David.

[#7]

Bear in mind that the functionality of our spam filters will be reduced because all of your email will be coming to us via the same collection of x10hosting mail servers. As you've found out, one of things our anti-spam appliances will do is check the reputation of the server that hands mail over to our network. Some aspects of our spam filtering will still work mind you.