A client asked me for my email adress to send me job instructions and files. I denied and said that he can send me the files via Upwork messenger or any online storage cloud.
So, is sharing an email for receiving files allowed?
Direct answer: Yes, you can communicate with your client via Email, and also share files through a file site like Dropbox or Google.
We are allowed to use any form of communication our clients prefer. This can be email, Skype, some other chat program like Slack, phone, etc.
In fact, it's 100% recommended that you set up an alternative way to communicate with your clients, because the Upwork Message Center goes down often.
Also a good idea to have an alternative file sharing tool as well, for the same reason.
You can share information with your client through email. You can use different ways to communicate and exchange files with your client, it's best to submit all work and contract negotiations through the Upwork platform and Messages. This way your communication is easily documented in case an issue arises. Also, it's important that all payments are made on Upwork.