Why am I not able to send or receive certain email attachments?

As a security measure to prevent potential viruses, Gmail doesn't allow you to send or receive executable files (such as files ending in .exe). Executable files can contain harmful code that might cause malicious software to download to your computer.

***You can send and receive messages up to 25 megabytes (MB) total including attachments. Any message that exceeds this limit will not be delivered and will be returned to the sender.***

Please see the Google Support article located here for additional info.