As a developer or QA tester, you need hundreds of test accounts. Using Gmail is slow (verification codes, 2FA). Using public temp mail gets you blocked. With a custom domain generator, you can automate account creation using test1@qa.yourdomain.com , test2@qa.yourdomain.com , etc., receiving verification links instantly without hitting spam traps.
You point your domain’s MX records to SimpleLogin, allowing you to create on-the-fly aliases that forward to your real address. email generator temp mail with custom domain