Receive 406 error when editor's plugins are enabled and external url enterred

Hi there,
I received a 406 error with both ckeditor or tynimce.
Just trying to put an external link (eg www.google.com) in the message body, save as draft, and error appear.
If editors plugins are disable, draft is saved, and all is fine.

Phplist v3.6.15
Ckeditor 2.7.1
TyniMCE v2.4.2

@vz777 Possibly the server has some anti-malware software that doesn’t like the html content of the campaign. The usual suspects are apache modsecurity and wordpress wordfence plugin.

@duncanc Thanks for answer
I don’t use wp, maybe when I have more time I’ll have a look at modsecurity, but I don’t remember configuring anything special on that side.

Anyway, have founded a solution

For external links, just put the link without the protocol, something like
I can’t explain why there’s a problem with external links but not internal links, but it works.