What Mailbox Providers Measure, and Who on Your Team Owns Each Part

Mailbox providers decide what to do with your mail from a handful of signals. None of them belongs to one person. Marketing controls who gets mailed and how often, whoever runs your domain's DNS controls the authentication records, and your sending platform (your ESP, or whoever runs your mail servers) controls how the mail is sent and how bounces and complaints are processed. When delivery slips, the fastest fix comes from knowing which of those three can act.

The Seven-Step Delivery Model splits this work between sender and platform. This article goes one level down and splits the sender's side across the people in your team.

The roles

• Marketing: whoever decides who is on the list, what is sent and when. In a small business, that may be you.
• DNS owner: whoever can change your domain's DNS records. Often IT, a web agency or the person who registered the domain.
• Sending platform: your ESP, or the team running your own mail servers. It sends the mail, signs it, and processes bounces and complaints.

At a glance

Complaints

What providers measure: how often recipients mark your mail as spam. Gmail asks senders to keep the spam rate reported in Postmaster Tools below 0.1% and never let it reach 0.3% (Gmail sender FAQ). Yahoo asks for below 0.3%, calculated on mail delivered to the inbox (Yahoo). Google says frequent spam reports make your future messages more likely to be marked as spam and, over time, lower your domain's reputation (Gmail sender guidelines).

Marketing owns why people complain: mailing people who didn't sign up, mailing more often than they expected, or making unsubscribing hard. Gmail requires marketing messages from senders of more than 5,000 messages a day to include a clearly visible unsubscribe link in the body (same source).

• First action: get the spam rate in front of you. Postmaster Tools shows it for mail to personal Gmail accounts, once your domain is verified (Google). Your DNS owner adds the verification record. Then compare complaints by mailing to find the ones that generate them.

The platform owns processing complaints and the unsubscribe mechanics. M3AAWG says ESPs must have a system to handle both feedback-loop messages and direct complaints (M3AAWG Senders BCP). Gmail requires one-click unsubscribe for marketing and subscribed messages from senders of more than 5,000 messages a day (Gmail sender guidelines). Yahoo requires it of bulk senders, recommends the POST method defined in RFC 8058, and asks that unsubscribes be honoured within 2 days (Yahoo).

• First action: confirm with your platform that complainers are suppressed automatically and that your marketing mail carries one-click unsubscribe headers.

Engagement

What providers measure: whether people read and act on your mail. Yahoo says sending email to people who are not reading it "will harm your delivery metrics and reputation" (Yahoo). Google suggests that senders "consider unsubscribing recipients who don't open or read your messages" (Gmail sender guidelines).

Marketing owns this signal: the targeting, the frequency and the offer.

• First action: define "inactive" by clicks or purchases rather than opens alone. Apple's Mail Privacy Protection downloads remote content "regardless of whether you engage with the email" (Apple), so a recorded open does not show that anyone read the message. Then follow what both providers suggest. Yahoo recommends periodically sending inactive subscribers a reconfirmation email (Yahoo), and Google suggests periodically confirming that recipients want to stay subscribed, and considering unsubscribing those who don't open or read your messages (Gmail sender guidelines).

List Hygiene and Sunset Policies covers how to set that up.

Bounces

What providers measure: how much of your mail goes to addresses that don't exist. M3AAWG says the volume of permanent failures "is one indicator used by receivers to build a reputation about a sender", and that a receiver will often penalise a sending IP for too many of them (M3AAWG Senders BCP). Microsoft's policy is that after a permanent (5xx) error, the sender must not try that message to that recipient again (Outlook.com postmaster policies).

The platform owns processing bounces: retrying temporary failures, suppressing permanent ones, and removing addresses that keep bouncing. M3AAWG considers it best practice to remove an address that bounces consecutively at least two times over two weeks or more.

• First action: confirm with your platform that addresses which bounce permanently are suppressed automatically.

Marketing owns what gets added. M3AAWG links large volumes of hard bounces to "a poorly managed registration process or an old or misapplied mailing list", and Yahoo recommends confirmed opt-in to reduce invalid recipients (Yahoo).

• First action: never re-import addresses your platform has suppressed, and confirm new addresses at signup.

Spam traps

What providers measure: whether you mail addresses nobody signed up with. Spamhaus describes a spam trap as an address "traditionally used to expose illegitimate senders who add email addresses to their lists without permission", which also identifies marketers "with poor data collection and list management practices" (Spamhaus, Email Deliverability 101).

Marketing owns this signal, because it comes from how addresses were collected and kept. Spamhaus advises putting the effort "into fixing the data collection, retention and hygiene problem, and not into trying to locate the spamtrap" (same source).

• First action: audit where your addresses come from. Stop mailing any segment that was bought, or that was collected without confirmation and hasn't been mailed in a long time. Google tells senders not to purchase email addresses (Gmail sender guidelines).

Spam Traps explains the trap types.

Authentication

What providers measure: whether your mail proves it comes from your domain. Gmail requires SPF or DKIM from all senders, and SPF, DKIM and DMARC from senders of more than 5,000 messages a day, with the From domain aligned with the SPF or DKIM domain (Gmail sender guidelines). Yahoo requires the same of its bulk senders (Yahoo), and Microsoft requires it of domains sending more than 5,000 emails a day to Outlook.com (Outlook.com postmaster policies).

Three people share this signal, and it breaks when one of them isn't told.

The DNS owner publishes the records.

• First action: run the domain check and fix anything bad. If there is no DMARC record, publish one with a reporting address. M3AAWG says any DMARC record, even one with p=none, should include at minimum a rua tag for aggregate reports, and recommends p=reject as the policy where possible (M3AAWG Email Authentication BCP). Reading a Domain Check Result explains each verdict.

The platform supplies the values to publish and signs the mail.

• First action: confirm that it authenticates your domain's email with SPF and DKIM, as Google asks senders who use a provider to verify (Gmail sender guidelines). The platform also runs the sending infrastructure the providers check, such as valid forward and reverse DNS for sending IPs and TLS connections (same source).

Marketing knows which tools send mail as your domain.

• First action: list every service that sends as your domain (newsletters, CRM, billing, the support desk) and give that list to the DNS owner. Google says your SPF record should include all email senders for your domain, and that mail from senders left out is more likely to be marked as spam (same source).

Volume patterns

What providers measure: how steady your sending is. Google advises sending at a consistent rate, avoiding bursts, and avoiding sudden spikes without a history of large volumes: "immediately doubling previously sent volumes suddenly could result in rate limiting or reputation drops" (Gmail sender guidelines). M3AAWG says consistency of volume "plays an integral part in the determination of IP reputation and deliverability outcomes" (M3AAWG Senders BCP). Spamhaus notes that sudden changes in mail volume are typical of infected hosts, and that providers react accordingly (Spamhaus, Email Deliverability 101).

Marketing owns the plan: a seasonal peak, a reactivation campaign, a newly imported segment.

• First action: tell your platform before any send much larger than usual, and build up to it over several sends rather than in one day.

The platform owns the sending rate: throttling, backing off when a provider defers mail, and warming up new IPs. Google advises reducing volume when messages start bouncing or being deferred, then increasing slowly again (same source). Outlook.com provides SNDS, which gives the owner of an IP range data such as mail volume and complaint rates for traffic from those IPs (Microsoft SNDS FAQ). If you send from your platform's IP addresses, the platform is the one that can see that data.

• First action: confirm the platform slows down automatically when a provider defers mail.

Related

• Is This a Delivery Problem? How to Tell Before You Spend Money — using these signals to decide what to do next
• The Seven-Step Delivery Model — the sender and platform split, and the campaign loop
• Foundations of Email Deliverability — why complaints and engagement weigh the most
• Gmail Email Sender Guidelines, Yahoo Sender Requirements and Microsoft Sender Requirements — the provider rules in full
• Google Postmaster Tools — the dashboard for the Gmail signals