Email platform Flodesk launched a Deliverability Center on October 13. It shows members the status of their domain authentication, which inbox provider rules they meet and how healthy each list is. Kendrick Wang, Flodesk's product manager for deliverability, put the job simply: "Inbox placement comes down to authentication, compliance, and engagement." You can run the same checks yourself, whatever platform you use.
Why it matters now
The big mailbox providers no longer just recommend good sending habits. They enforce them.
Google's sender FAQ says that "Starting November 2025, Gmail is ramping up its enforcement on non-compliant traffic," with temporary and permanent rejections for mail that misses its requirements. Email consultant Al Iverson flagged the change on Spam Resource when Google added it. Microsoft says domains sending more than 5,000 emails a day to Outlook.com accounts must pass SPF, DKIM and DMARC. Since May 5, 2025, mail that fails goes to junk and may be rejected if the issues are not fixed. Yahoo has enforced similar standards since February 2024.
For lead generation teams, the cost is direct. A lead you paid for is worth little if your follow-up email lands in spam.
1. Authenticate your sending domain
How: Check your DNS for SPF, DKIM and DMARC records. Google and Yahoo ask bulk senders to set up both SPF and DKIM, plus a DMARC policy of at least p=none. Microsoft accepts p=none but recommends p=reject. Google recommends 2048-bit DKIM keys.
Source: Google email sender guidelines, Yahoo Sender Hub, Microsoft Outlook postmaster policies.
2. Align your From address and check the plumbing
How: The domain in your From: header must align with either the SPF or the DKIM domain, according to Google and Yahoo. Microsoft says alignment with both is preferable. While you are in DNS, confirm your sending IPs have valid forward and reverse DNS records, and that mail is sent over TLS, which Google requires for all senders.
Source: Google email sender guidelines, Yahoo Sender Hub, Microsoft Outlook postmaster policies.
3. Watch your spam rate, not just your open rate
How: Set up Google Postmaster Tools for your domain and check the user-reported spam rate. Google says to keep it below 0.1% and avoid reaching 0.3%. Above 0.3%, bulk senders are ineligible for mitigation, Google says. Yahoo also sets its line at 0.3%.
Source: Google email sender guidelines FAQ, Yahoo Sender Hub.
4. Make leaving easy
How: Add a list-unsubscribe header that supports one-click unsubscribe for marketing mail, and keep a visible unsubscribe link in the body. Yahoo says to "Honor unsubscribes within 2 days." Google recommends acting on requests within 48 hours. A clean exit is cheaper than a spam complaint.
Source: Yahoo Sender Hub, Google email sender guidelines and FAQ.
5. Clean the list before you send
How: Google advises that senders "Automatically unsubscribe recipients who have multiple bounced messages" and consider removing people who do not open or read their mail. It also says to confirm each address before subscribing it, and not to buy email addresses from other companies.
Source: Google email sender guidelines.
6. Ramp up slowly on new domains and lists
How: If a domain or list has no sending history, start small. Google says to begin with a low volume sent to engaged users, increase it slowly, and avoid sudden spikes. Flodesk's new tool builds a four-step warming plan for the same reason.
Source: Google email sender guidelines, Flodesk.
What this means for lead generation teams
Deliverability starts at the form, not the send button. Every address that enters your CRM either helps or hurts your sender reputation. Confirm addresses at sign-up, as Google advises, and make sure every contact actually asked to hear from you. If you buy leads, ask how each one was verified and how consent was captured before it reached you. That question sits at the heart of verified lead generation, one of the services ADFLU runs.
Then put the six checks on a calendar. Authentication rarely breaks on its own, but domain changes, new tools and new subdomains can quietly undo it.
"Email is a direct line to customers, and that line only works if the message gets through," said Flodesk co-founder and CEO Rebecca Shostak.
The bottom line
The rules are public, and the major providers are enforcing them. Spend an hour on these checks before your next campaign and you protect every lead you paid for. Expect the tools to get sharper: Flodesk says complaint rate reporting and mailbox performance by inbox provider are next.
