How does an email actually get delivered?
Through a chain of servers using SMTP, guided by DNS — and the important structural fact is that email is a store-and-forward system with no guarantee of delivery and no reliable confirmation of failure.
The sequence:
You submit the message from a client to your provider's submission server, authenticated, usually on port 587.
Your provider looks up the recipient domain's MX records in DNS, which list the mail servers accepting mail for that domain, with priority values.
It connects to the highest-priority MX host and delivers the message over SMTP, opportunistically encrypting the connection.
The receiving server evaluates it — SPF, DKIM and DMARC checks, reputation of the sending IP address, content analysis, and blocklist checks.
It is placed in a mailbox, a spam folder, or rejected, and this decision is entirely the receiver's.
You retrieve it by IMAP, POP or a web interface — which are retrieval protocols, not delivery protocols, a distinction that confuses people constantly.
What happens when it fails:
Hard bounce — permanent, such as an address that does not exist, returned as a delivery status notification.
Soft bounce — temporary, such as a full mailbox or rate limiting, where the sending server queues and retries over hours or days.
Greylisting, where a receiver deliberately rejects a first attempt temporarily on the reasoning that spam software rarely retries. This is why some mail arrives minutes late.
Silent discard, which is the worst case and is common: some receivers accept a message and then delete it without notifying anyone, so the sender believes it was delivered.
Why email is unreliable in ways people do not expect:
Delivery is best-effort. There is no guarantee, and read receipts are a request the recipient may ignore.
The receiver decides everything, and reputation is built over time by sending behaviour.
Encryption is opportunistic by default, so a hop may be unencrypted unless the sender requires otherwise.
Forwarding breaks authentication, which is why forwarded mail lands in spam more often.