# Foundations of Email Deliverability

> The core principle of deliverability — sending wanted and expected email — and how mailbox providers measure it.

Source: emailmarketing.net — https://emailmarketing.net/learn/foundations/foundations-of-email-deliverability

Mail reaches the inbox when the people receiving it both want it and expect it. The two conditions are different, and each one counts:

1. **Wanted**: the message gives the recipient something they value.
2. **Expected**: the recipient recognizes the mail, because they signed up for it or already do business with your brand.

## How mailbox providers evaluate your email

No mailbox provider or internet service provider (ISP) can ask each recipient whether a message was welcome. What a provider can do is watch how its users treat your mail across tens of thousands of mailboxes, and that behaviour is a more reliable answer than asking. Complaints and engagement weigh the most. For each campaign, a provider can see:

- The share of recipients who reported it as spam
- The share who deleted it unread
- The share who opened and read it
- How much time readers spent on it

Filtering algorithms combine these measurements into a judgement on whether recipients want and expect mail from you.

## Content matters too

Recipient behaviour is not the whole picture. Providers also scan what a message says when they decide whether it is spam, and certain words or phrasing can count against it.

## Technical details matter

How you send is judged as well. Spam filters take into account:

- The number of connections you open to each receiving domain
- Email authentication (SPF, DKIM and DMARC, see [DMARC](https://emailmarketing.net/learn/authentication/dmarc))
- How you warm up new IP addresses (see [IP Warm-Up](https://emailmarketing.net/learn/ip-management/ip-warm-up))

You set these in your MTA or other sending infrastructure, whichever mail server software you run.

## Important caveats

- The final decision belongs to the mailbox provider: the Inbox, the Spam folder, or refusing the message. Good practice makes your mail the kind a provider is willing to deliver to the Inbox, but no practice can promise Inbox placement.
- Expect to adjust in rounds, because improving deliverability is an **iterative process**. Each campaign adds to your sending history, and that data shows what to change next.

## Related articles

- [Two Worlds of Email Deliverability](https://emailmarketing.net/learn/strategy/two-worlds-of-email-deliverability), on the principle of wanted and expected email in more depth
- [IP Warm-Up](https://emailmarketing.net/learn/ip-management/ip-warm-up)
- [Basic IP Allocation](https://emailmarketing.net/learn/ip-management/basic-ip-allocation)