Some CSS properties are known for their poor support across various email clients and should generally be avoided. These include:
Positioning: Properties like position, float, and z-index are often ignored or poorly supported. Advanced selectors: Complex selectors like :nth-child and :hover may not work as expected. Background images: The background-image property is not consistently supported. Web fonts: Custom fonts via @font-face are not supported in many email clients. Media queries: While some email clients support media queries, many do not, making responsive design challenging.