Some Domains not delivering correctly

I have a server picking up four domains. Each connects via the Pop
Connector to the global mailbox for that domain and downloads the mail.
Now this is working fine on two domains but not the other two, one of
which is the main domain. If I turn off the SMTP service I can see the
mail appearing in the Pickup folder and they look fine there. As soon
as I turn the SMTP back on they seem to just disappear. If I telnet
into the server and try sending an email direct that way with mail
from:, etc then it arrives. Can anyone assist?

Kind regards,

Mark

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