Domains.
We buy domains in bulk from Porkbun and Cloudflare. Namecheap is fine but Porkbun is cheaper at scale. We run 30-60 domains per client depending on volume. Don't overthink it - just grab variations of the main brand: .co, .io, .net, .org. Cloudflare for the ones we need more control over, Porkbun for the rest.
One thing that's changed in 2026: Google's brand new domain penalty got worse. Used to be you could send after two weeks of aging. Now you're looking at three to four weeks minimum before it's safe to send any real volume. Plan for it or you'll burn domains in week one.
Inbox providers.
This is where most agencies die. Setting up hundreds of inboxes manually will literally kill you and your sanity. We used to do it ourselves and it was the worst part of running the agency by far.
Now we use three different inbox providers depending on what we need. All in the same space (pre-warmed cold email inboxes) but each has its own strengths.
Mailscale for Google Workspace heavy clients. Solid product, been around longer than most. Pricing is fine, their warmup network works.
Zapmail when we need to spin up infrastructure fast - like a new client signs Monday and wants to launch by Friday. Zapmail can deliver and you're live in days, not weeks.
Puzzleinbox for most of our Outlook 365 volume. Pre-warmed inboxes shipped in 24-72 hours with SPF, DKIM, DMARC already configured. Their WhatsApp support is genuinely the fastest in the space - matters when a client's inboxes go down at 11pm on a Friday. We have about 600+ inboxes with them right now across clients.
Honestly, all three are good. Anyone telling you there's only one inbox provider worth using probably has an affiliate link. We mix and match based on niche, channel split (Google vs Outlook), and timeline.
What I won't do anymore is self-warm inboxes. Used to spend three weeks warming new inboxes per client. Now we just buy pre-warmed. The maths doesn't even make sense to self-warm in 2026 - you're paying staff to babysit warmup tools when you could have pre-warmed inboxes shipped to you.
Sending platform.
Instantly for 90% of campaigns. Smartlead is the other option and it's solid too - honestly a coin flip between the two. Pick one and master it, stop switching every three months like half the agencies I see. We tried Bison briefly. Not for us but some agencies love it.
Inbox rotation, unified inbox, campaign analytics - all standard stuff but you need a tool that does it well or you can't scale past a few clients.
Lead lists and data.
Apollo for the basics. Cheap and the data is fine for most ICPs. Ocean.io when we need lookalikes - actually really good for finding companies similar to a client's best customers. Clay for enrichment when we need to layer signals. Expensive but worth it for higher ticket clients. BuiltWith and Storeleads for tech stack and ecom filtering.
We also use a few niche scrapers depending on the client. LinkedIn Sales Navigator exports + Phantombuster for some campaigns. Not going to name all of them because honestly some are sketchy and I don't want to recommend them publicly.
Email verification.
Emaillistverify and Millionverifier. We've used both. emaillistverify is what we use now - faster and cheaper at our volume.
never ever skip verification. Bounce rate above 3% and your domain is cooked. I've seen agencies skip this step to save twenty quid and burn five hundred quid worth of domains. Don't be that guy.
We verify twice actually. Once when the list is built. Once right before send. Yes it costs more. Yes it's worth it.
Copywriting and AI.
Claude for most copy work. ChatGPT for some research. But honestly we write 90% of the copy ourselves and use AI to iterate, not to generate from scratch. The agencies that have AI write the whole email all have the same problem: their emails read like AI wrote them. Prospects can tell. Reply rates suck. Use AI for variations and personalisation angles. Don't use it to write your whole first email.
CRM and reporting.
HubSpot for clients who already have it. Pipedrive for smaller clients. We push hot replies into the client's CRM via Zapier or Make depending on what's needed.
For our own reporting we built a custom dashboard in Airtable that pulls from Instantly and the client's CRM. Shows pipeline generated per client per month. Clients love it. Churn dropped massively when we started showing £ instead of meetings.
Now here's what's actually changed in 2026 that most people aren't talking about:
Outlook overtook Gmail for cold email deliverability in some niches. This would have sounded insane 18 months ago. But Microsoft loosened up. Google tightened. For certain ICPs (enterprise B2B especially) Outlook is now the better channel. We're running 60/40 Outlook to Google on most clients now. It was the opposite two years ago.
Google's AI is reading your emails now. gmail's new categorisation is way more aggressive. If your email looks templated it goes straight to Promotions. Don't care if you 'warmed up properly'. The AI is looking at the email content itself. Short. Plain. one ask. Human voice. Anything else gets filtered.
DMARC enforcement got real. As of February 2026, Microsoft and Google are both enforcing DMARC on outbound. p=none doesn't cut it anymore for high volume senders. If your DMARC isn't set up properly, your inboxes are getting throttled silently. half the agencies complaining about 'deliverability issues' just have bad DMARC records.
The 15 emails per inbox per day rule. Used to be 30-40 per day was fine. Not anymore. We're keeping it at 12-15 per inbox per day per workspace. Yes that means more inboxes. Yes that means more cost. But reply rates went up about 40% when we made the switch.
Reply rate quality scoring is the new game. Google and Microsoft are tracking positive vs negative reply ratios on your inboxes. Too many 'stop emailing me' replies and your inbox gets soft suspended even with low bounce. We now actively remove anyone who replies negatively from all future sequences across all clients. One strike, one removal. Our deliverability got noticeably better when we started doing this.
Anyway, that's the stack. Works for us. Might not work for everyone. But if you're still self-warming and sending 50 a day from a single domain, you're going to have a bad time.
