📄 Article
✓ Link checked
Free
Beginner
Why we picked it
This is Google's own rulebook for what gets an email into Gmail instead of spam: SPF or DKIM for every sender, SPF, DKIM, and DMARC together once you send any volume, valid reverse DNS, and TLS in transit. When you are debugging why your cold email is landing in spam, this is the primary source to check yourself against, not a vendor's interpretation of it.
From
Google (Gmail/Workspace support)
- Gmail requires SPF or DKIM for all senders, and SPF, DKIM, and DMARC together for bulk senders
- Your DMARC domain must align with the domain in your From header
- Keep your Postmaster Tools spam rate under 0.30 percent or Gmail may reject or spam your mail
Open
support.google.com →
📄 Article
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Free
Beginner
Why we picked it
Postmark is an email delivery company, so this is a working list from people who watch inboxes for a living, not a generic checklist. It walks through the concrete, boring reasons emails get flagged: missing authentication, no plain text version, shortened links, no unsubscribe link, and mismatched subject lines and content. Good first stop before you touch any DNS record.
From
Postmark
- Missing SPF or DKIM is one of the fastest ways to get flagged as spam
- Always send a plain text version alongside HTML, spammers often skip it
- Avoid URL shorteners and use full, branded links instead
Open
postmarkapp.com →
📄 Article
✓ Link checked
Free
Intermediate
Why we picked it
Spam complaints are the signal that actually poisons a domain, more than any single email landing in a spam folder. This piece explains what a complaint rate is, how mailbox providers use it, and concrete ways to keep it low. Read it once you have SPF, DKIM, and DMARC set up and want to protect the reputation you just built.
From
Postmark
- A complaint rate above roughly 0.1 percent starts hurting your sender reputation
- Make it obvious who you are and why you are emailing, confusion drives complaints
- Monitor complaints per domain, not just overall, so one bad list does not sink everything
Open
postmarkapp.com →
📄 Article
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Free
Intermediate
Why we picked it
Mailgun is one of the infrastructure providers that actually sends the mail, so this is a hands-on, technically accurate walkthrough of what each DNS record does and how to add it, not marketing copy. Use it as your step-by-step when you are actually setting up SPF, DKIM, and DMARC for a new domain rather than just reading about the concepts.
From
Mailgun
- SPF, DKIM, and DMARC are separate DNS TXT records that each do a different job
- DKIM cryptographically signs your message so receivers can verify it was not altered
- Start your DMARC policy at p=none with reporting on before moving to quarantine or reject
Open
mailgun.com →
📄 Article
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Free
Beginner
Why we picked it
HubSpot sends a genuinely enormous volume of email and publishes what they tell their own customers to do to stay out of spam. It is a clean checklist covering authentication, list hygiene, and engagement monitoring, useful as a second, ESP-side view alongside Google's own sender guidelines.
From
HubSpot Knowledge Base
- Connect and authenticate your sending domain with SPF and DKIM before you send at any volume
- Regularly prune unengaged or invalid contacts, they drag your sender reputation down
- Watch your open and click rates over time as an early warning of a reputation problem
Open
knowledge.hubspot.com →
📄 Article
✓ Link checked
Free
Intermediate
Why we picked it
Instantly is built specifically for cold outreach, so this guide is framed around your exact problem rather than transactional email in general. It explains Gmail and Outlook's current bulk sender rules and gives specific record examples, which is useful once you already understand the basics and want the cold-email-specific version.
From
Instantly
- Gmail and Outlook now enforce SPF, DKIM, and DMARC for anyone sending meaningful volume
- Keep your SPF record under 10 DNS lookups or it silently fails
- Set DMARC reporting up first so you can see problems before you enforce a strict policy
Open
instantly.ai →
📄 Article
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Free
Beginner
Why we picked it
This directly supports the 'warm up a fresh domain slowly' half of your answer. It lays out why a brand-new domain has zero reputation with mailbox providers, why that takes longer to build than warming up a single mailbox, and a realistic timeline, rather than the extreme 'no warmup needed' claims some vendors make.
From
Woodpecker
- A new domain has no sending history, so providers treat it with suspicion by default
- Domain warmup takes longer than mailbox warmup, plan for weeks, not days
- Never send a large campaign to untargeted prospects on a domain that has not been warmed
Open
woodpecker.co →
📄 Article
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Free
Intermediate
Why we picked it
This is the clearest explanation of exactly the advice in your short answer: keep cold outreach off your main domain so a spam hit never touches your team's real email. GlockApps is a deliverability testing company, so the reasoning here is grounded in how reputation actually gets tracked per domain, not just intuition.
From
GlockApps
- A separate cold email domain keeps spam complaints from ever touching your primary domain's reputation
- Your main domain's transactional and internal mail stays protected no matter what happens to outreach
- You still have to warm and authenticate the separate domain properly, it is not a shortcut around good hygiene
Open
glockapps.com →
📄 Article
✓ Link checked
Free
Intermediate
Why we picked it
This gives you a week-by-week volume ramp for a new domain alongside the authentication basics, which is more concrete than most guides that just say 'go slow.' It also covers content-side traps like too many links or images that trip filters even when your DNS is perfectly configured.
From
Mailshake
by Mark Lindquist
- Ramp sending volume gradually over roughly 6 weeks rather than jumping straight to full volume
- Watch your bounce rate closely, pull back if it goes over about 5 percent
- Keep early cold emails light on links, images, and attachments
Open
mailshake.com →
📄 Article
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Free
Intermediate
Why we picked it
Ajay Goel has built email sending software for two decades, so this guide connects deliverability mechanics to the practical realities of running a cold email campaign end to end. It is a good bridge between the technical setup and actually writing and sending your first sequence.
From
GMass
by Ajay Goel
- Deliverability, list quality, and copy all interact, weakness in one undermines the others
- Test your setup with a free email tester before sending to real prospects
- A clean, engaged list matters as much as your DNS records for staying out of spam
Open
gmass.co →
📄 Article
✓ Link checked
Free
Advanced
Why we picked it
Al Iverson spent 15 years running deliverability for a major email platform, and this is his running commentary on what mailbox providers are actually doing right now. Once you have the basics working, this is where the real, current edge cases live: mailbox provider policy changes, blocklist behavior, and DMARC enforcement shifts that generic guides do not track.
From
Al Iverson
by Al Iverson
- Deliverability rules change over time as Gmail, Outlook, and Yahoo tighten policy, treat any static guide as a snapshot
- Authentication is necessary but not sufficient, sending behavior and complaint rates matter just as much
- Blocklists and reputation systems are opaque by design, so building margin matters more than chasing a perfect score
Open
spamresource.com →
📄 Article
✓ Link checked
Freemium
Intermediate
Why we picked it
A tactical follow-on covering the channels and motions top B2B startups scale after the first ten. Grounds distribution strategy in real company examples.
From
Lenny's Newsletter
by Lenny Rachitsky
~15 min read
- Content/SEO is a surprisingly dominant B2B channel (Vanta, Amplitude, Figma, HubSpot).
- The core B2B channels: self-serve inbound, sales-assist inbound, outbound, content, paid, partnerships.
- Pick and systematize the one channel that compounds for you.
- Distribution strategy should follow evidence, not fashion.
Open
lennysnewsletter.com →
📖 Book
✓ Link checked
Paid
Intermediate
Why we picked it
This is the book most modern cold outbound advice quietly borrows from, so reading the source is worth it. Its "Cold Calling 2.0" idea flips the usual pitch: instead of selling in the first email, you send a short, plain email asking who the right person is, which is far harder to delete because it asks for a small favor, not your time. It is more about the system behind outbound than clever subject lines, which is why founders keep coming back to it.
From
Amazon
by Aaron Ross and Marylou Tyler
~208 pages
- The best cold email often asks for a referral to the right person rather than pitching, which lowers the reply barrier
- Short, plain, non salesy emails outperform polished marketing copy in cold outbound
- Outbound works as a repeatable process, not a one off blast, so structure and follow up matter more than any single line
Open
amazon.com →
