Hosted mailboxes and transactional relays solve different problems. This overview shows where each kind of service fits and links straight to the providers.
You need mailboxes
People read and write mail in an inbox. A hosted mailbox provider handles storage, calendars and contacts, and is the right choice for staff and personal addresses.
You need to send from an application
Receipts, password resets and alerts come from software. A transactional relay accepts them over SMTP or an API and takes care of delivery and bounce handling.
Hosted mailboxes
Providers for everyday email.
Hosted mailboxes
Fastmail
Mailboxes, calendar and contacts for people and teams, with custom domain support. Built for reading and writing mail, not for sending application traffic.