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550 Validating Sender

Ok, I have a customer that I host e-mail and web for.  They have three domains they have e-mail for that I host on my mail server (using hmailserver).  Each domains MX record points to a third party SPAM filter (MXLogic).  They can send/receive mail just fine.  However.....

They also have e-mail accounts they use from one of their customers.  They make citrix connection to their other e-mail and try sending e-mail from their to one of the accounts I host and they get a 550 Validating Sender failure message.  I tried googling this but there is virtually nothing out there.  Any ideas?
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lkingpinl
Asked:
lkingpinl
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1 Solution
 
CPAsAdminCommented:
Is the citrix server using an Exchange server or are they pointing directly to the ISP's smtp server?  
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CPAsAdminCommented:
If they have their own mail server on the citrix network, I would suspect that their reverse dns is not set to their domain name.
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lkingpinlAuthor Commented:
You are correct.  My mailserver flagged it as spam because of that.  I whitelisted them for now and alerted them of the issue.  Thanks.
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