What If a Client Doesn't Have an Email Address?

A unique email address is required for every user.  This ensures that the session history is always valid and unique for that listener.  One way to set up a unique email for a client that doesn't have one is to create an alias email.  Each email provider has an option to create aliases.

There are quite a few ways to create multiple email addresses in Gmail.

For instance, if your email address is hello@gmail.com, any email that’s addressed to either he.ll.o@gmail.com or hello+world@gmail.com will also be delivered to your main inbox since Gmail ignores dots and anything that’s after the plus symbol in email usernames.