Why some times iZip does not open my email attachment?

iZip supports to open many files types, including: zip, gz, rar, pdf, doc, xls, ppt, txt and video, audio files from your email. 

Due to a known issue on iOS, some files with extra "."  or other special characters such as "-" in file names could fail to be opened in other Apps. This happens on not only iZip but all other Apps. 

If you can remove the extra "." or other special characters from the file name, iOS will be able to handle it.