Bug in Gmail’s SMTP Server or bug in Apple Mail?

Today I tried to send a zip file to a client (I’m using Google for Domains so I use their SMTP and IMAP server) and was unable to do so through Mail.app. It got part way through the transfer and said it couldn’t send it. After a bit of trial and error, I discovered the problem. I use Hazel to automatically move files and set the color of items so I know what is new. When I created the zip archive, Hazel automatically colored it. I reset the Finder label and presto, the file went through.