Hello,
it seems that the issue is caused by the unfortunate way how iCloud Private Relay feature Apple has added to MacOS Monterey is implemented.
The workaround is to go to Mail -> Preferences -> Privacy and disable both "Protect Mail Activity" and "Hide IP Address". Or you have to click on "Load Content Directly" on the top of the email for every email. Or disable Avast Web Shield.
Detailed description:
In MacOS Big Sur, Apple has discontinued kernel extensions for implementing network filters, like Avast Web Shield or Avast Mail Shield; instead a new mechanism (Network Extension framework of System Extension functionality) was added. The Network Extension framework allows multiple vendors to add their own security and privacy specific filters to the same connections on the same machine, thus allowing coexistence and cooperation of such 3rd party products.
Unfortunately, Apple has decided to not use this functionality in their Monterey implementation of Private Relay functionality and to make it mutually exclusive with Network Extension based extensions - a very unfriendly and anti-competitive thing to do.
What is going on: In case a mail contains HTML mail body, Apple's Mail app uses HTTP(S) to load various elements (like pictures). Avast's Web Shield component is registered in Network Extension to be notified about all HTTP(S) connections; for web browsers, it processes such connections transparently; for other connections (including those from Apple Mail) it tells Network Extension: "I am not interested, pass the connection through". Unfortunately, the mere fact that Network Extension is configured to be notified about HTTP(S) connections causes Private Relay to be disabled even for those it does not actually process.
Apple Mail detects that the connection did not go through Private Relay, and displays the following line on the top of the mail: “Your network preferences prevent content from loading privately.” and a button "Load Content Directly".
Please note that this issue is not unique to Avast; this is unavoidable if MacOS decides to not pass the connection through Private Relay. It is also not connected with scanning of emails per se, rather it is simply a "messaging issue" by Apple Mail. We are not yet 100% sure about all the details when this happens.
We have filed multiple reports to Apple, asking them to allow coexistence of 3rd parties with their own solutions, as well as asking them to fix this issue somehow. We have also used our direct channel to notify them about the issue.
We are currently analysing what else we can do, as this state is awful. We apologise deeply for the issues; however there is currently no good solution to this.
Kind regards,
Ondrej Kolacek