SpaceBarb

Your link didn't work. Can I contact customer care via email? And is there a case number I should reference?

Marcos, I don't know what any of it means or how one thing relates to another. SSL, ports, protocol, etc. It's all foreign to me. But this inability for Dropbox to connect started about a week ago, and as far as I know, the only thing that has changed in my system(s), is that both Dropbox and ESET perform automatic updates in the background. So I assume that one of those updated with something that's now incompatible.

Marcos, thanks for the reply. In "Web Access Protection", under HTTP where I unchecked "Enable HTTP protocol checking", the list of "Ports used by HTTP protocol:" had 80,8080,3128,443. I tried removing 443 (because you didn't mention it in your reply) and enabling HTTP protocol checking, but Dropbox would not connect. Unless someone has a better solution, disabling that seems to be the only way to make it work.

FOR MAC USERS: After searching and searching for a solution to why my Dropbox was giving me the error "can't establish secure internet connection", (and after talking to Dropbox support), and after finally getting to chat with an ESET tech support person, the following solution worked. Open ESET Cyber Security preferences, click "Web Access Protection" and UNCHECK "Enable HTTP protocol checking". ALSO, go to "General", "Exclusions: Setup...", under "File System" click the plus sign and find your Dropbox application in your Applications folder to add in the list. THEN, also click "Web and Email", then under "Display exclusions:" go to "Applications" and also add the Dropbox application there. Click "OK". Both might not be necessary, but that's what got Dropbox connecting and synching again for me.

FOR MAC USERS: After searching and searching for a solution to why my Dropbox was giving me the error "can't establish secure internet connection", (and after talking to Dropbox support), and after finally getting to chat with an ESET tech support person, the following solution worked. Open ESET Cyber Security preferences, click "Web Access Protection" and UNCHECK "Enable HTTP protocol checking". ALSO, go to "General", "Exclusions: Setup...", under "File System" click the plus sign and find your Dropbox application in your Applications folder to add in the list. THEN, also click "Web and Email", then under "Display exclusions:" go to "Applications" and also add the Dropbox application there. Click "OK". Both might not be necessary, but that's what got Dropbox connecting and synching again for me.