Kaspersky engine fails to download updates, causing the plugin to continuously fail to initialize. The update servers are accessible. Autoupdate logs report the following:
2020-07-20,16:17:46,092,1,"#00003550","#0000000B","info ","autoupdate","download_vendor: DOWNLOADFINALSTATE: DOWNLOADERROR"
2020-07-20,16:17:46,092,1,"#00003550","#0000000B","info ","autoupdate","download_vendor: UPDATEFINALSTATE: UNKNOWN"
You need to ensure free HTTP/HTTPS traffic to the GFI update servers listed below.
Firstly, you must allow fallback to HTTP for the downloads, as described in the Setting MailEssentials to use HTTP to download updates article.
It has been observed that content firewalls may interfere with the download of the updates, by blocking parts of the definition files. If that happens, the effects can be unpredictable. Manually updating the definitions as instructed in the How to manually update Kaspersky Definitions article will only solve the problem temporarily, as the next automatic update will most likely encounter the issue again.
If that is the case, make sure that there aren't any firewall rules or any content firewalls that might prevent access to the update servers. GFI MailEssentials downloads updates from the following locations over HTTP ports 80 and 443: