Except your client does not live in a bubble. It needs to communicate and send emails to other clients.

In order to combat spam, many popular email providers rank messages using an array of criteria, coming from a known and well publicised email provider is one such criteria and not coming from a well known provider is one such criteria that redirects your email to many people's spam folders.

So the question remains, how do we ensure that nostr relays don't start to use exclusionary metrics to avoid spam and abuse?