As another user pointed out - I use the separate email addresses for separate side projects. Some have additional team members on the ___domain, some have just me.

I used to try and run them all under one email client, but it got messy to try and keep replies separate and coming from the correct ___domain address (for support and marketing queries etc.). Also, trying to run one inbox on mobile was achievable, but tricky.

I like having each web app ___domain in a totally separate, sandboxed inbox. Occasionally I delegate the handling of a particular inbox to another team member for a week or two while I am either away or working on a project, so it is nice to be able to attach/detach an Inbox from my conscious management whenever I like.

In order to redirect, you still need smtp server for the ___domain. Also if these are for some side ventures, handling correspondence via single inbox can be bit inconvenient and error-prone.