I am unable to download from my gmail account. I get the message that I am not connected to the server. However another account works just fine and I can connect to the internet with no problems. From the internet I am able to access my gmail account.
When you say another account do you mean Gmail account ? I had this recently at a customer where their firewall did some funky things because they used the GoogleCloud as their business environment so I assume they connected through to a different part of Gmail. Everything else worked fine just retrieving and updating email. If I cared I VPN’d out to my corporate environment and was fine.
Yes, anti-virus/firewall or VPN applications can block some accounts depending on e.g. which port they are using to connect to the server. You can check this by temporarily disabling the anti-virus/firewall application or VPN and see if there is any difference.
But also eM Client was having some issues with Gmail in recent versions. I believe the most recent release addresses these, so if you are not using it, you can download it from the Release History.