Industry Guide Marketing
An email that is delivered can still land in spam. Authentication, low complaint rates, easy unsubscribes and steady sending decide whether your emails reach the inbox.
Email deliverability is whether your messages reach the inbox rather than the spam folder, or are rejected outright. It is different from the "delivered" figure in most email platforms, which only means the receiving server accepted the message. A campaign can show 99% delivered and still land largely in spam.
Deliverability matters more than it used to. Since 2024, the largest mailbox providers have published firm requirements for bulk senders, and they enforce them. For an online store, poor deliverability means promotions and order-related messages that customers never see. For a B2B company, it means nurture sequences and event invitations that quietly stop working. This guide explains the current requirements, the factors that decide inbox placement and a practical routine for testing and monitoring.
Gmail. Google's email sender guidelines set requirements for everyone sending to personal Gmail accounts from February 1, 2024, including SPF or DKIM authentication and keeping spam rates reported in Postmaster Tools below 0.3%. Senders of more than 5,000 messages a day to Gmail accounts must also publish DMARC for their sending domain (a policy of "none" is accepted), and marketing and subscribed messages must support one-click unsubscribe with a visible unsubscribe link in the body. Google recommends keeping the spam rate below 0.10% and never reaching 0.30%.
Yahoo introduced comparable requirements for bulk senders at the same time, covering authentication, one-click unsubscribe and low complaint rates.
Microsoft Outlook. For domains sending 5,000 or more messages a day to Outlook.com, Hotmail.com and Live.com addresses, Microsoft requires passing SPF and DKIM and a published DMARC policy of at least "none," aligned with SPF or DKIM. As summarized by the DMARC provider dmarcian, non-compliant bulk messages have been rejected since May 5, 2025, rather than filtered to junk.
Even if you send fewer than 5,000 messages a day, meet the bulk sender requirements anyway. Volumes grow, promotions spike, and the practices that satisfy the rules are the same practices that keep mail out of spam.
Authentication proves that mail claiming to come from your domain really does.
Many companies discover through DMARC reports that several tools send mail as their domain without authentication. Fix those before tightening the policy, or you will block your own invoices and password resets.
Spam complaints are among the strongest signals mailbox providers use. A complaint rate is complaints divided by messages delivered to that provider. For example, 200 complaints from 100,000 messages delivered to Gmail is 0.2%: above Google's recommended 0.10% and close to its 0.30% limit.
Ways to reduce complaints:
Be careful with opens as an engagement measure. Apple's Mail Privacy Protection, introduced in 2021, can load images automatically, which records opens that never happened. Clicks, replies, purchases and site visits are more reliable signals of real engagement.
Mailbox providers distrust sudden changes. A new domain, a new IP address or a list that has not been mailed in months should be warmed up gradually, starting with your most engaged subscribers and increasing volume over several weeks.
Separate your mail streams where it makes sense: transactional messages such as receipts and password resets on one subdomain, marketing on another, and any sales outreach on a third. A problem with promotional mail then does not affect order confirmations.
Before peak periods such as Black Friday, raise volumes gradually in the weeks before rather than tripling them on the day. Our Black Friday email and SMS checklist covers the campaign side.
Before sending:
Ongoing monitoring:
| Symptom | Likely cause | First check |
|---|---|---|
| Sudden drop in clicks at one provider | Filtering to spam at that provider | Postmaster or SNDS data; seed tests |
| Messages rejected with authentication errors | Missing or failing SPF, DKIM or DMARC | Message headers; DMARC reports |
| Rising spam complaints | Unexpected frequency, unclear sign-up, purchased contacts | Recent list sources and send frequency |
| Many hard bounces | Old or unvalidated list | List source and last mailed date |
| Good opens but few clicks | Machine opens inflating figures | Compare click and conversion trends |
The following scenario is invented for illustration.
An online homeware store sends weekly promotions to 120,000 subscribers. Clicks from Gmail recipients have fallen by a third, while other providers are stable. Postmaster Tools shows a spam rate around 0.25% on promotion days.
The team finds that 45,000 subscribers have not clicked in over a year and that pop-up sign-ups did not say how often emails would arrive. It sends a re-engagement sequence to the inactive group and stops mailing those who do not respond, adds frequency information to sign-up forms, introduces a welcome email and moves inactive subscribers to a monthly digest. It also adds DMARC to the sending domain and moves receipts to a separate subdomain. It then raises volume gradually before its peak promotions and watches spam rate by provider daily.
Content matters less than reputation and authentication, but it still plays a part:
Email deliverability is the ability of your messages to reach recipients' inboxes rather than spam folders or being rejected. It depends on authentication, sender reputation, complaint rates, list quality, sending patterns and content.
Send to seed accounts at the main mailbox providers or use an inbox placement testing tool, then check where each message lands. Combine that with ongoing data from Google Postmaster Tools, Microsoft SNDS and your platform's bounce and complaint reports.
Some rules apply to everyone sending to Gmail, such as SPF or DKIM authentication and a low spam rate. The stricter requirements, including DMARC and one-click unsubscribe, apply to senders of 5,000 or more messages a day. Meeting them anyway is good practice and protects you as volume grows.
Check your domain's SPF, DKIM and DMARC records this week, set up Google Postmaster Tools and look at your spam rate by provider. Those three checks reveal most deliverability problems.
Growix's Email & SMS Marketing team runs campaigns and automated sequences that customers actually read, and our Retention & Lifecycle Marketing team builds the re-engagement and lifecycle programs that keep lists healthy. To decide how your email effort should be split, see email newsletters vs automated email flows.
With weeks to go, Black Friday email and SMS results depend on deliverability, consent, a clear sequence and margin-aware measurement. A checklist dated to the 2026 calendar.
Campaigns and newsletters drive moments; automated flows work every day in the background. Build the few flows that matter first, then decide how much campaign effort you need.
More form fills rarely fix a thin pipeline. Define what a qualified lead is, offer something buyers want, score and nurture what comes in, and judge every channel by pipeline.
