I am employed by a consulting company (let's call them Initech), and have been deputed to work for a client (call them Acme). I have been working out of Acme's office, almost since the time Initech hired me. I am the only Initech employee working for Acme (other Initech employees work for other companies).
I have now resigned from Initech, and would be leaving them in about a week's time. At my previous jobs, I have sent a "goodbye" mail to my colleagues on the last day as a custom/etiquette (which I believe is quite prevalent anyway).
This is, however, my first job as a consultant, and I am in a predicament. It doesn't feel right to "just pack your stuff and leave" without sending the goodbye email. There isn't anyone at Initech whom I could send this mail to, since the only people with whom I have had some interaction are my manager (whom I am going to thank separately anyway), and 3 guys who interviewed me (all of whom have already left Initech).
All my work relationships on this job have been with Acme's employees. However, I am not sure if sending such emails to a client's employees is considered good etiquette. I don't want to bother my Initech manager with this question, he certainly wouldn't bother either way.