Who are the main players in email delivery?
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When you hit send on an email, it doesn't just fly straight from your desk to someone's inbox. It passes through a chain of players, each doing a specific job. Knowing who they are makes it a lot easier to figure out what went wrong when something does.
Here's how they break down.
Senders. That's you. Whether you're a one-person newsletter or a company blasting out a million receipts a day, you're the one responsible for what gets sent and to whom.
Email Service Providers (ESPs) are the platforms you send through. Think Mailchimp, Klaviyo, or Postmark for transactional email. They give you the sending infrastructure, the analytics, and the compliance features so you don't have to run your own mail servers. Your ESP is the one actually pushing your messages out over SMTP on your behalf.
Mailbox Providers (MBPs) are where your email lands. Gmail, Outlook, and Yahoo Mail are the big three. They receive incoming messages, run them through spam filters and reputation checks, and decide whether your email ends up in the inbox, the spam folder, or nowhere at all. MBPs hold a lot of power in this chain.
Blocklists and anti-abuse networks sit in the background as reputation arbiters. Organizations like Spamhaus maintain lists of IPs and domains known for sending spam, phishing, or malware. MBPs consult these lists during filtering. If your sending IP is on one, your emails are going to have a hard time getting through regardless of how great your content is.
Standards bodies write the rules everyone else follows. The IETF publishes the core protocols. M3AAWG is the industry group where ESPs, MBPs, and security researchers collaborate on abuse prevention. They're why authentication protocols like SPF, DKIM, and DMARC exist and got widely adopted.
The big picture is that all these players talk to each other constantly. Your ESP connects to MBPs using SMTP. MBPs check blocklists in real time during that connection. Anti-abuse networks share intelligence across the industry. And standards bodies publish the protocols that hold it all together.
And if your email isn't arriving where it should, the answer is usually hiding somewhere in this chain.
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