Whether you're launching a cold outreach campaign or ramping up your marketing automation you'll want to avoid pitfalls and SPAM traps. Email deliverability can make or break your results. If you're not landing in the inbox, you're invisible. And if you're not playing by the rules, you might not be sending at all.
In this guide, we’ll build on our recent discussion around using HubSpot’s Sales Sequence module for one-to-one email outreach. We’ll take it a step further and walk through a deliverability-first mindset, blending strategy with tactical tips so you can stay compliant, credible, and convert-worthy.
Your email sending reputation is a hidden score that inbox providers (like Gmail and Outlook) assign to your domain and IP address. It’s built on how recipients interact with your emails. Open rates, spam complaints, bounce rates — all of these factor in.
Strong reputation? Your emails get a front-row seat in the inbox. Weak score? Say hello to spam folders and email blocks.
| Area | Key Actions |
|---|---|
| Authentication | Set up SPF, DKIM, and DMARC records for your domain |
| Gradual Volume | Warm up new domains/IPs slowly to avoid suspicion |
| List Hygiene | Proactively validate emails and remove undeliverable, unengaged and bounced addresses regularly |
| Spam Avoidance | Don’t use misleading subject lines or image-only emails |
| Engagement Monitoring | Track opens, clicks, bounces and complaints to stay proactive |
| Reputation Checks | Monitor via Google Postmaster Tools or Talos Intelligence |
Think of domain authentication like a passport. Without it, inbox providers treat your emails as shady or unverified. Here’s what to get right:
| Protocol | Purpose | Tools |
| SPF | Confirms who can send emails for your domain | MXToolbox SPF, Google SPF Guide |
| DKIM | Adds a digital signature to your messages | DKIM Overview |
| DMARC | Tells inboxes how to handle unauthenticated messages | DMARC Analyzer |
| BIMI | Lets you display your brand logo in supported inboxes | BIMI Group |
| Feature | Why It Matters | Check Tools |
| Custom Subdomain | Protects your root domain’s reputation | Mailgun's Guide |
| Dedicated IP | Essential if you send 100K+ emails per month | HubSpot Dedicated IP |
| Reverse DNS | Matches sending IP to your domain | GlockApps SMTP Test |
| TLS Encryption | Keeps email transit secure | SSL Labs Test |
You can have perfect setup, but if you're sending to junk contacts, you're toast. List quality directly affects engagement rates and complaints.
| Action | Why It Matters | Tool Examples |
| Double Opt-In | Ensures consent and cuts bounces | Double Opt-In Explained |
| List Cleaning (proactive email validation) | Keeps you off blacklists and traps/ "Don't wait for the bounce" | ZeroBounce, NeverBounce |
| Suppress Inactive Contacts | Improves engagement averages | HubSpot Unengaged List Guide |
| Monitor Metrics | Early warning for reputation damage | Google Postmaster, Postmark |
Content can sink your deliverability even if everything else is perfect. Keep it human, useful, and real.
| Tactic | Why It Helps |
| Avoid ALL CAPS or Clickbait | Looks spammy and triggers filters |
| Add a Plain Text Version | Improves inbox placement & accessibility |
| Optimise for Mobile | Many opens happen on phones |
| Test Before Sending | Spot spam triggers & rendering issues |
Tools like GlockApps or Mail Tester can give you a heads-up.
Deliverability is a moving target. Gmail, Outlook, and others constantly update filters. Stay ahead with regular checks.
| Tool | Purpose | |
| Google Postmaster | Reputation and delivery monitoring for Gmail | |
| Blacklist Monitors | Check if you’ve been flagged globally | MXToolbox Blacklist |
| Inbox Testing | Know where your email lands | Email on Acid |
If you have a new domain, then don’t start cold. A warm-up schedule helps build sender trust with inbox providers.
Start small, monitor constantly, and scale thoughtfully. External email domain warming tools might also be a good shout if you plan on ramping up your outreach efforts. See ZeroBounce's warm up service as an example.
Good deliverability isn’t just a technical task—it’s strategic. It intersects with your GTM plan, your messaging quality, and your operational discipline.
If you're running outreach from HubSpot (or any platform), take deliverability seriously. It's the hidden engine behind successful email programs, and it deserves your attention.
Whether you're emailing 50 people or 50,000, your ability to land in the inbox is what gets you heard. And that starts with doing things the right way, from day one.