Hi aus9
Email providers are quite capable of looking inside .zip, .rar, .bz, .gz, etc
files to examine the source code and .tcz files.
When examining the source code, variable and function names as well
as programming language syntax can trigger the spam filter.
When examining the .tcz file, regardless of whether it knows how to look
inside it, there is always the possibility of a false positive on the virus scan.