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It produced this output:
When client clicked link in email they got an error in Safari warning them that the site was not safe. Client did not provide more detailed info
They were able to access the site by typing mediamix.tv in their browser and then clicking on the “Our Work” link which leads to the same URL that was contained in the emai,
My web server is (include version): Apache/2.4.18 (Ubuntu)
The operating system my web server runs on is (include version): Ubuntu 16.04.1
My hosting provider, if applicable, is: SELF HOSTED
I can login to a root shell on my machine (yes or no, or I don’t know):
I’m using a control panel to manage my site (no, or provide the name and version of the control panel): ISPCONFIG
Can you show the actual link your customers received in their emails?
(I specifically asked it that way because they may not have received exactly what you sent)
Your SSL/TLS configuration is compatible with Safari versions as old as the one shipped with Mountain Lion, so this is likely a local issue.
This is not what Safari says when it encounters an SSL error. It says "Safari cannot verify the identity of the website" on Macs and "Cannot Verify Server Identity" on iOS. If "this site was not safe" is the actual text of the error your client received it is likely they have some malware or toolbar that is interfering with normal Internet access on their system.
In light of what @Patches found, it would be great to somehow get a screenshot from the user who’s having the problem in order to try to understand what the exact error is.