If your email deliverability strategy hasn't changed since 2023, you're probably losing inbox placement and don't know it. Google and Yahoo rolled out strict new sender requirements in 2024, and the enforcement has only tightened since. Microsoft followed with its own requirements in early 2025. What was optional best practice two years ago is now mandatory.
Here's what's changed and what you need to do about it — based on what I've seen across dozens of HubSpot portals sending millions of emails monthly.
Authentication is no longer optional
SPF, DKIM, and DMARC were always recommended. Now they're required. If you're sending more than 5,000 emails per day to Gmail addresses without proper authentication, your emails are going to spam or getting rejected entirely.
SPF (Sender Policy Framework) tells receiving servers which IP addresses are authorized to send email on behalf of your domain. If you're using HubSpot, your SPF record needs to include HubSpot's sending servers.
DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your emails proving they haven't been tampered with in transit. HubSpot provides DKIM keys that you add to your DNS records.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) tells receiving servers what to do with emails that fail SPF or DKIM checks. A DMARC policy of "none" is the minimum — it enables reporting without blocking emails. But the direction of travel is clear: mailbox providers increasingly favor senders with "quarantine" or "reject" policies.
If you haven't set these up, stop reading and do it today. Everything else in this article is irrelevant if your authentication is broken. HubSpot has a step-by-step guide to email domain authentication that walks you through the DNS setup.
The spam complaint threshold is lower than you think
Google now enforces a spam complaint rate threshold of 0.10% — that's one complaint per thousand emails. Cross 0.30% and you'll see serious deliverability damage. These numbers are lower than most marketers realize.
The practical implication: every email you send to someone who doesn't want it increases your complaint rate. Purchased lists, outdated contacts, and re-engagement campaigns sent to cold databases are the fastest ways to destroy your sender reputation.
Monitor your complaint rate through Google Postmaster Tools. If you're not already using it, set it up — it's free and gives you direct visibility into how Google perceives your sending domain.
One-click unsubscribe is mandatory
Bulk senders must include a one-click unsubscribe mechanism in their email headers. This isn't the unsubscribe link in your email footer — it's a List-Unsubscribe header that mailbox providers use to show an "Unsubscribe" button directly in the email client.
HubSpot handles this automatically for marketing emails, which is one less thing to worry about if you're on the platform. But if you're sending transactional emails through a different service, verify that your List-Unsubscribe headers are properly configured.
The logic is straightforward: if people can easily unsubscribe, they're less likely to hit the spam button. A clean unsubscribe is always better than a spam complaint.
List hygiene is your highest-ROI activity
I've seen companies agonize over subject lines and send times while sitting on a contact database where a large portion of addresses are invalid. List hygiene isn't glamorous, but it's the single highest-impact thing you can do for deliverability. It's part of a broader data quality practice that affects every part of your CRM.
Remove hard bounces immediately. HubSpot does this automatically, but verify it's working. A hard bounce is a permanent delivery failure — the address doesn't exist. Continuing to send to hard bounces signals to mailbox providers that you don't maintain your list.
Suppress unengaged contacts. If a contact hasn't opened or clicked an email in six months, stop sending to them. They're either not interested or the address is abandoned. Either way, sending to them hurts your metrics.
Run regular verification. Use an email verification service to check your database quarterly. Tools like ZeroBounce or NeverBounce can identify invalid, disposable, and risky email addresses before they damage your reputation.
Sending infrastructure matters
If you're on HubSpot's shared IP pool, your deliverability is partially affected by other senders on the same pool. For most companies, this is fine — HubSpot actively manages its shared infrastructure. But if you're sending high volumes (100,000+ per month) or have strict deliverability requirements, consider a dedicated sending IP.
A dedicated IP means your reputation is entirely your own — for better or worse. You'll need to warm it up gradually, starting with your most engaged contacts and slowly increasing volume over four to six weeks. Skip the warmup and you'll be flagged as a suspicious new sender.
Also consider your sending subdomain. Many organizations now use a dedicated subdomain for marketing emails (e.g., email.company.com) to isolate marketing reputation from transactional email reputation. If your product notification emails are critical and can't risk deliverability issues from a marketing campaign, separate your sending domains.
Content still matters, but differently
Spam filters in 2026 are less about keyword triggers and more about engagement patterns. Sending emails that get opened, clicked, and replied to improves your reputation. Sending emails that get ignored or deleted hurts it.
That said, some content practices still help: keep your text-to-image ratio reasonable (don't send image-only emails), avoid excessive links, use a consistent "From" name that recipients recognize, and write subject lines that accurately describe the content. Clickbait subject lines might boost open rates short-term, but they increase complaints and unsubscribes.
The best deliverability strategy is also the simplest: send relevant content to people who want to receive it. A well-designed marketing automation system helps you do exactly that — right message, right time, right person. Everything else is technical scaffolding to support that principle.
Your deliverability checklist
If you do nothing else, make sure these are in place: SPF, DKIM, and DMARC configured and passing. Google Postmaster Tools set up and monitored. Spam complaint rate below 0.10%. Hard bounces removed automatically. Unengaged contacts suppressed after six months. List verification run quarterly. One-click unsubscribe headers in place.
Get these fundamentals right and you'll outperform most senders. And once your emails are reaching inboxes, make sure your lead scoring model is working so the right follow-up happens at the right time. Deliverability isn't about tricks or hacks — it's about discipline and consistency.
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