Many email services let you create aliases, which are basically extra email addresses which forward to your inbox. This way people can reach you without needing to know your main email address.
For example your email address might be email@example.com, but you could create aliases such as firstname.lastname@example.org or simply email@example.com.
You might even create aliases to log into specific services such as firstname.lastname@example.org. Emails sent to these addresses will appear in your main inbox, so you don't have to monitor multiple accounts.
If you're systematic with your aliases it's easy to tell where your spam is coming from. From there it's not difficult to change one alias without abandoning your main inbox.
Using aliases also offers an extra level of security against hacking attempts. Someone trying to break into your Paypal account won't get far if they're using email@example.com but your login is firstname.lastname@example.org.