Hello,
unfortunately this is a long time problem caused by Apple's issue in the design of the mechanism in which their iCloud Relay system works in Apple Mail. It has been reported to them and escalated several times, but with no solution at this moment.
What is the core of the issue: When you display your email, it can link to resources (like images) which are located at the internet. Thus the mail client functions as a browser. And if iCloud Relay is enabled for the mail client, it checks whether some other software is filtering content of web pages on the machine (like our Web Shield does); if it detects such software, it knows that due to the way how they have decided to implement the relay system in iCloud Relay the connection will not actually travel through the relay system, and causes the Mail client to report this to the user via forcing you to allow each message to load manually.
The irony is that while our Web Shield intercepts web (HTTP/HTTPS protocol) connections from the Mail client, it immediately detects that it originates in Apple Mail and decides to not process the connection. But due to the way how Apple has decided to implement the technology, that does not matter.
There are two possible solutions:
1) disable Avast Web Shield component
2) disable iCloud Relay in Apple Mail.
We apologise for the problems this has caused you.
Kind regards,
Ondrej Kolacek
