Working with a webhost to tighten their security settings to get PCI compliant. In doing so we ended up breaking many of their clients email access by turning off SSLv3 and TLSv1.0. I was given the task of helping all the clients fix this issue (see seperate blog post for the fix). One in particular ended up not having issues beyond the normal problems with TLS and it turned out being ESET Antivirus. Here is the story:
Unable to Access Website:
The client first mentioned that they could not access a particular website that they needed to submit government paperwork. The error was related to the certificate being out of date. I checked the site on my own computer and it came up just fine, so looked at their certificate and it was current with plenty of time left before expiring. Cleared the cache and all the normal troubleshooting steps to no avail, so had to dig deeper. Remembered that some antivirus programs scan HTTPS traffic by putting their own certificate in place of the actual certificate from the site. Looked inside ESET Antivirus and found the culprit. Under Internet Protection > Web Access Protection I turned off the HTTPS Scanner. Restarted the browser and was able to surf to the site without issues.
Hidden Messages Stuck in Outlook Outbox:
The client then mentioned that some messages weren’t sending, so looked into it and found a couple messages that were 2MB+ which I told them were too large to send. We got rid of those but then messages were still stuck but were now hidden from view. I used the typical fix for read receipts that are hidden using the MFCMAPI tool but found nothing there. Tried removing the account and re-adding it to Outlook. After the clients 8,000+ emails downloaded via IMAP the same problem began occurring again. Remembering the issues with ESET Antivirus web filtering, I decided to take a look at that again. Under Internet Protection > Email client protection I turned off all the Email Clients, Email Protocols, and Antispam Protection. Restarted Outlook and the problem persisted. Had to remove the account and re-add it to Outlook. After the clients 8,000+ emails downloaded via IMAP the problem was fixed.
All that being said, these kinds of problems are another reason that I recommend Webroot to my clients for their antivirus protection. I prefer to have the Website filtering happen at the DNS level via a company like DNSFilter.com and the SPAM / Email filtering to happen via the email provider or an email protection service like Mailprotector.com.
If your company is interested in using a real layered approach to security not just putting a software band-aid on it, then contact us for assistance.