Basic and Advanced Cold Email Deliverability Checklist for 2025
This year, a significant change in our deliverability strategy has centered on using ESP matching. This is where you match the type of inbox you use (Outlook, Google, Zoho, etc.) to that of your recipient.
But further than this, our guide here will share (almost) everything we’ve seen recently, from the must-do basics to advanced tactics that keep your emails landing where they should: The primary inbox.
We've split this guide into two sections:
A quick checklist to cover your essential cold email setup.
A more advanced checklist based on real-world lessons from sending millions of cold emails.
Basic Email Deliverability Checklist for 2025
This checklist will be enough to get you started understanding email deliverability fundamentals in 2025. If you master each of these and consistently maintain them, you’ll be off to a flying start.
Please continue reading for our advanced email deliverability checklist for 2025.
Basic Email Deliverability Checklist | Elizma from The ProspectAgency
Verify Your Lead List
High bounce rates destroy sender reputation faster than almost anything. Bounces tell inbox providers your data is stale, untrustworthy, or scraped, which gets you flagged. Use tools like DeBounce to keep bounce rates low and sender reputation intact.Use SPF, DKIM, and DMARC Records
These email authentication protocols are non-negotiable for deliverability. Cold outreach should never come from your primary domain (e.g., yourcompany.com). One spam complaint or poor reply rate can damage your brand's inbox placement across all email activity.
Instead, set up dedicated domains (e.g., yourcompany-outreach.com) with matching aliases and signatures. It keeps your core infrastructure safe while still on-brand.Send From Dedicated Domains
Always send outbound emails from separate, correctly set-up domains to keep your core domain safe. Inbox providers treat brand-new domains with suspicion, and if you start sending cold emails right away, they'll assume you're spam.
Let domains age for at least 30 days before launching campaigns. In that time, you can begin setting up inboxes and warming them up gradually.Wait 30 Days Before Sending (for Newly Registered Domains)
Email accounts don't just "work" out of the box. Cold inboxes need to mimic natural usage; sending small volumes, receiving replies, and avoiding mass outreach. Domains registered recently need at least 30 days to age. Like fine wine, the older the better.Warmup for at Least 14 Days (Ideally 30)
Even an excellent copy can contain hidden spam triggers, like too many links, specific keywords ("free," "guaranteed," "act now," etc.), or technical issues in the header. Use warm-up tools (e.g., Instantly) to build the sender's reputation gradually.Use Spam Checkers (Like Mailmeteor's or Mail-Tester)
Before sending, this can help catch content and technical issues that trigger spam filters.Utilise Spintax
Spintax (e.g., {Hi|Hey|Hello}) adds variation to your cold email templates so that each message looks slightly different, and inbox providers don't see your campaign as a mass send. These help catch content and technical issues that trigger spam filters.Keep Emails Short, Human, and Personalised
Your cold emails should sound like someone writing to another, not a bot pitching something. Avoid long intros, fancy formatting, or overused phrases. Keep the tone conversational, relevant, and clear. Use custom intro lines or reference details from the lead's company or role.< 30 Cold Emails per Day per Account
You should never use the actual sending limit of email accounts; it's a fast track to being blacklisted. Inbox providers monitor daily volume closely. Even 30 is on the upper limit. Many pros start with 15–20 per day, then slowly scale up. Think marathon, not sprint. Inbox reputation takes time to build, and seconds to ruin.Run Regular Inbox Placement Tests (e.g., with GlockApps)
Just because your email was "delivered" doesn't mean it landed in the primary inbox. It could be in spam, promotions, or worse, not seen at all.
Advanced Email Deliverability Checklist for 2025
Now onto the advanced checklist. The following checklist is based on our recommendation, having sent tens of millions of cold emails since we started and observing recent, up-to-date trends.
Advanced Email Deliverability Checklist | Elizma from The ProspectAgency
This checklist is to be cautiously approached, as it may not be relevant again in the future.
No Domain Forwarding
Forwarding domains — where one domain redirects to your leading site — might seem like a harmless branding move. But it now poses a serious risk to deliverability.Here’s why: when someone marks your email as spam, it doesn’t just affect your sending domain; it can also impact your receiving domain.
Forwarding links tie the two together, meaning a single complaint can hurt your main domain’s reputation, even if you’re sending from a separate one. In addition, forwarding often leads to authentication inconsistencies (like SPF/DKIM mismatches), making it harder to pass deliverability checks.Stick to direct, clean domains with no redirects. Forwarding isn’t worth the risk.
Send Cold (and Warm) Emails On Saturdays (but Not Sundays)
Saturday sending is one of the easiest inbox hacks. Fewer companies send on weekends, so your message faces less competition, often boosting open and reply rates. It also helps warm-up algorithms track natural, consistent engagement across the week. Sundays, however, are hit-or-miss. Engagement is low, and cold inboxes often go ignored.Send 18 Cold Emails per Day per Account
While conventional advice caps sending at 30/day, our data shows that 18/day per inbox is a safer, more sustainable volume, especially on younger domains. It mimics natural sending behaviour, keeps bounce rates down, and helps you scale gradually without attracting Gmail or Outlook spam filters. Slow, consistent sending beats, fast, risky scaling.< 3 Email Accounts per Domain
Each domain has a shared sender reputation across all connected inboxes. Using too many accounts from a single domain (especially for outbound) risks collective penalties. Once one gets flagged, the others suffer too, even if their content is clean. Stick to a maximum of 3 active senders per domain to stay under the radar and maintain quality.
2 Dedicated IPS per Admin Workspace
Using tools like IP Royal, assign a different static IP to each email account you manage and a separate one for admin logins (where you monitor deliverability, tweak copy, etc.), this prevents inbox providers from detecting "suspicious behaviour" (like multiple logins from the same IP) and helps preserve domain trust. IP hygiene is one of the most underrated factors in long-term deliverability. Don't overlook it.ESP Matching (Google to Google, Outlook to Outlook)
ESP-to-ESP matching matters more than most people realise. Over the past seven months, we've consistently seen Outlook underperform, especially when sending from Google to Outlook or even Outlook to Outlook.
Even with premium Azure IPS, performance has been spotty at best, and still doesn't come close to Gmail-to-Gmail deliverability. Ironically, Google to Outlook sometimes outperforms Outlook's internal network, but results are inconsistent and often disappointing.
If deliverability is a priority (and it should be), we recommend favouring Gmail-based sending where possible and treating Outlook with caution unless necessary. Choosing the wrong ESP match can quietly tank your performance, even if everything else is done right.
Conclusion
What used to be "good enough" is now a fast track to the spam folder. Use this checklist to pressure-test your setup. Inbox placement is invisible until it's too late — check it early, fix it often, and send with confidence.
Want a done-for-you setup that follows all these best practices (and more)? Contact The ProspectAgency, we're here to help you send smarter, scale safely, and book meetings that matter.
