When I started running cold email for B2B companies in the early 2010s, there was no checklist. There was trial and error, client complaints, and the particular frustration of watching a well-crafted campaign disappear into spam folders without explanation.
This is not a generic list pulled from a deliverability blog. Every item represents either something I got wrong and paid for, something a client got wrong and I had to fix, or something I watched founders ignore until it became a crisis.
Before You Send a Single Email
These are not optional. If any of these are missing or misconfigured, nothing else on this list matters.
Never send cold email from your primary business domain. Set up a dedicated sending domain — e.g. if your main domain is tacticalism.com, use tactic.email or tacticalism.io. Protect your main domain reputation from cold outreach variability.
Sender Policy Framework tells inbox providers which mail servers are authorised to send on behalf of your domain. Check yours with MXToolbox. If it is missing or has errors, fix it before anything else.
DomainKeys Identified Mail adds a cryptographic signature to your outgoing email. Inbox providers use this to verify the email was not altered in transit. Your email sending platform will provide the DKIM record — add it to your DNS and verify it.
DMARC tells inbox providers what to do when SPF or DKIM checks fail. At minimum set p=none to monitor failures. Graduate to p=quarantine, then p=reject as your infrastructure matures.
Newly registered domains have no reputation history. Inbox providers apply extra caution regardless of how well everything else is configured. If your sending domain is less than 30 days old, plan for a longer warmup period before expecting consistent inbox placement.
Set up a custom tracking subdomain for open and click tracking. Default tracking domains from email tools are shared across all users — if other users have poor sending practices, your tracking domain shares their reputation damage.
Domain Warmup
Automated warmup tools create detectable patterns that inbox providers are increasingly flagging. Manual warmup using real human inboxes is the only approach that builds durable reputation in 2026.
Minimum four weeks before running any cold outreach campaigns. Six to eight weeks is safer. The impatience to start sending before the domain is warmed is one of the most common and most expensive deliverability mistakes.
The emails sent during warmup should generate real replies — not automated responses, not just opens. Real human interactions signal to inbox providers that this domain is associated with genuine communication.
List Quality
Scraping LinkedIn, buying from data brokers, or using unverified databases are the fastest paths to poor deliverability. The quality of your contact list determines your engagement rates — which directly determines your domain reputation.
Run every list through an email verification tool before sending. Remove hard bounces, spam traps, and invalid addresses.
Bounce rate above 2% sends a strong negative signal to inbox providers. Above 5% can trigger immediate reputation damage.
~40% of domains use catchall configurations, meaning verification tools return "catchall" rather than "valid" or "invalid." Sending to unverified catchall addresses generates hard bounces. Either use a tool that verifies catchall addresses specifically, or exclude them from cold outreach entirely.
Everyone who has unsubscribed or asked not to be contacted must be on a permanent suppression list.
Spam complaints above 0.1% trigger significant deliverability issues. Above 0.3% you will be blacklisted.
Campaign Configuration
Maximum 50 emails per day per inbox for cold outreach. If you need higher volume, add more inboxes rather than pushing a single inbox above safe limits. Volume above this threshold is a primary trigger for spam filtering.
Send during business hours in the recipient's timezone. Emails sent at 3am local time generate lower open rates, signalling lower engagement to inbox providers. Monday to Thursday performs better than Friday for most B2B audiences.
In 2026 the evidence is clear: plain text cold emails outperform HTML emails on deliverability and reply rate. HTML formatting, images, and multiple links are all associated with marketing emails and spam in the filters inbox providers apply to cold outreach.
If you include a link, include one. Every additional link increases spam score and reduces the likelihood of inbox placement. If you need to share more, include them in replies after an initial response.
Include a simple unsubscribe option in every cold email. In many jurisdictions this is legally required. More importantly, a visible unsubscribe option reduces spam complaints — recipients who want to opt out can do so cleanly rather than clicking "report spam."
Monitoring and Maintenance
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Use MXToolbox or a similar tool to check whether your sending domain or IP appears on major blacklists. Blacklist inclusion happens faster than most founders expect and requires immediate action when detected.
Google Postmaster Tools provides direct visibility into how Gmail treats your domain — domain reputation, IP reputation, spam rate, and authentication pass rates. If you are not monitoring this, you are flying blind on deliverability to Gmail inboxes, which represent the majority of B2B email addresses.
Even well-managed sending domains accumulate reputation signals over time. Rotating to fresh sending domains every quarter — while maintaining warmup discipline — keeps your deliverability infrastructure fresh and reduces the risk of accumulated negative signals.
Reading the data.
Every deliverability problem leaves a trail. Sudden open rate drops, rising bounce rates, increased spam complaints, blacklist appearances — these are signals of a specific problem with a specific cause. Most founders look at declining metrics and change their email copy. The copy is almost never the primary cause. The infrastructure, list quality, or sending behaviour is. Build the habit of reviewing deliverability metrics weekly — not monthly, not when something goes wrong. Weekly.
Key takeaways
- The fundamentals haven't changed — what has changed is how quickly inbox providers detect shortcuts
- Before sending anything: custom domain, SPF, DKIM, DMARC, email verification, clean list
- Manual warmup only — 4 to 6 weeks minimum before cold outreach begins
- Plain text, one link, business hours sending, 50 emails per day per inbox maximum
- Monitor Google Postmaster Tools, blacklists, and engagement benchmarks weekly
- Fix the infrastructure, not the copy — deliverability problems always leave a trail
