We have discovered that some e-mails with attached .zip files sent by us to @gmail.com addresses are returned with a delivery error. Returned messages contain the following information in the message body:
Gmail won't accept these types of files even if they are sent in a zipped (.zip, .tar, .tgz, .taz, .z, .gz) format. If this type of message is sent to your Gmail address, it is bounced back to the sender automatically. http://mail.google.com/support/bin/answer.py?answer=6590
Please note this if you provide and send screens of errors, documents and other types of attachments in a zipped format. Use another format to archive your files (with another file extension), for example WinRAR program.