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Cisco ASA 5510 with specified domain address being blocked

Good day,

We have a Cisco ASA 5510 with Interscan for Cisco CSC SSM.

We have had a user complain that they up until recently used to receive emails from a specific person (email coming from vendor in Taiwan) but now have stopped receiving them altogether. The person in Taiwan is not sending any attachments with the email nor is doing anything different in sending the message. We know the message is not being filtered as there are no messages in our administrator email account stating it was blocked due to probhibited content or a security risk and we have added the email address to the POP3 antispam "Approved Senders" list. What is baffling is why the emails are no longer coming through from that email address. We have asked them to carbon copy the email to a web based email account and we have verified that it was received as a standard message with no attachments or inline images or anything at all other than text.

Could this be related to the senders IP being placed on a blacklist that the Cisco device uses?

I don't know what blacklist subscription the Cisco uses so if anyone could tell me where I can go to check to see if that IP is blacklisted and any info I would need if I find out they are and need to remove them from that list specifically for us then I would really appreciate it.

Or if anyone can think of any other reason this would be happening that would be a great help!

Thank you


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