Mail on your domain means your business does not read as a personal address on a free provider. It also means the DNS records that prove you are allowed to send are your responsibility, and that is the part most small businesses get wrong. We publish the records with you, verify alignment, and set a DMARC policy you can actually enforce instead of one that quietly fails open.
Transactional delivery is a separate concern from human mailboxes and we treat it that way. Password resets, receipts, and alerts should not share a reputation with a mailbox that also receives newsletters. The relay tier gives your application authenticated SMTP with its own credentials and its own sending domain alignment.