MarsEdit users who have not updated to MarsEdit 4 may encounter an error while trying to connect to blog servers that have been configured to require newer versions of TLS, the protocol that is used to create secure HTTPS connections between MarsEdit and your site.

Because of the way Apple’s networking infrastructure was designed, macOS does not use the latest version of TLS when running applications that were designed for earlier versions of macOS. If you are running macOS 10.12 or higher, the best solution to this problem is to upgrade to MarsEdit 4. You can download a free trial from the MarsEdit home page.

If you decide to keep using MarsEdit 3, the app supports an override preference that will force it to always use the newer version of TLS. The downside is if you also need to connect to web sites that are not updated to support the latest version of TLS, MarsEdit 3 will fail to connect to those sites after setting this preference. To set the preference, simply click this link to automatically open MarsEdit and register the setting. You can revert the setting by clicking this link.

If clicking the links above does not active MarsEdit, or if the setting doesn’t seem to change the behavior of your network connections from the app, you may need to manually set the preference from the Terminal application on your Mac:

1. Quit MarsEdit
2. Open Applications -> Terminal
3. Paste the following command, and press return to execute it:

   defaults write com.red-sweater.marsedit RSNetworkingEnableExperimentalTLSSupport 1

4. Reopen MarsEdit

You should now be able to connect to servers that require TLS 1.2.