When working on some client projects I've noticed that I need to create account pretty regularly or use them in newsletters to test the newsletter functionality.
I've also needed this to test the changes in the sign up process, upgrade, downgrade etc.

It's really important to test your (or your client's) app while logged in as a user/client because the admin account gives you access to everything you tend to forget how user's UI looks like.

I have started creating long and descriptive emails when I needed to test above mentioned features on my or clients' WordPress sites.
I am using gmail to catch all incoming emails. This works for G Suite customers as well.

When you work on ongoing projects at some point you come up with an abbreviation about each project that you use in emails and in ticketing system.

e.g. Awesome Client becomes AC.

I am adding a lot of information because I have multiple clients and staging WordPress sites so I need to know right away which site sent the email without checking the log files.

Let's assume that your main gmail account is: you@gmail.com

Here are how the emails look like depending on the environment.

development machine
slavi+clients+ac+dev@gmail.com

for staging
slavi+clients+ac+stg@gmail.com

for live
slavi+clients+ac+live@gmail.com

or you can include domain name as well

slavi+clients+ac+site+example.com@gmail.com

or
if you have to create accounts daily you can include the current date as well
slavi+clients+ac+site+example.com+2019+01+01@gmail.com