As a security measure to prevent potential viruses, Gmail doesn't allow you to send or receive executable files (files ending in .exe) that could contain damaging executable code.

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.

There is a work-around that involves renaming the file extension. Also, check with your intended email recipient to make sure that their system will allow receipt of email attachments.

You can send and receive messages up to 20 megabytes (MB) total (including attachments). Any message that exceeds this limit will not be delivered to your inbox and will be returned to the sender.

See Google help document http://mail.google.com/support/bin/answer.py?hl=en&answer=6590