If you run cold email for clients, deliverability is not a one-time setup, it is an ongoing operational cost. You have many sending domains, many mailboxes, and many clients who will blame you the moment their replies drop. The difference between an agency that keeps clients inbox-ready and one that constantly firefight is a boring, repeatable system: authenticate every domain, monitor every domain daily, and be able to show the client exactly what is happening. Here is that system.
Each client usually has their own sending domain (or a subdomain), their own ESP, and their own reputation. What works for one client does not automatically work for the next. The mistake is to assume a setup is "done" once and move on. A client's domain can silently break between campaigns: an SPF record loses its include when they switch ESPs, a DKIM key rotates, a DMARC policy gets tightened by mistake, or their sending IP gets blocklisted after a bad day. Any one of these drops their deliverability overnight, and if you only check when a client complains, you are always a week behind. The fix is to check every client domain on a schedule, not on demand.
Before a client's cold campaign goes out, confirm the sending domain passes the core checks. This is the same list whether the client is on Instantly, Smartlead, Lemlist, or sending manually:
1. MX routes to a real mail server (the domain can actually receive and process mail).
2. SPF includes the client's ESP and ends in -all (a missing -all is a common silent failure).
3. DKIM is actually signing, on the same domain as the From header.
4. DMARC is present and not accidentally set to reject (a mis-set reject bounces the client's own mail).
5. TLS/STARTTLS is available on the sending path (plain-text SMTP is a spam signal).
6. PTR / reverse DNS matches the sending IP (a missing PTR is a classic cold-email killer).
7. IP reputation is clean (not on a blocklist from a previous client's bad day on a shared IP).
The free cold email deliverability checker runs all seven in seconds and tells you exactly which record to fix. For a single domain that is enough. For a book of clients, you need the next part.
Campaigns are sporadic, but deliverability breaks are not. A record can expire on a Tuesday and the client will not notice until their Thursday campaign underperforms. Daily monitoring of every client domain catches the break on the day it happens, when it is a five-minute fix. You want a system that re-runs the full check on each domain every 24 hours and alerts you the moment a record changes, breaks, or an IP gets listed. That is the difference between "we noticed the drop and fixed it" and "we found out when the client called." Inboxproof Pro does this for up to five domains; the Agency tier covers up to twenty-five client domains under one account so you can run the whole book from one dashboard.
Clients do not want to read raw DNS. They want to know: is my domain ready, what is broken, and what did you do about it. A white-label deliverability report, branded with your agency's name, is the artifact that turns a technical check into a client-facing deliverable. It is the thing you attach to a "your domain is ready" email, the thing that justifies the retainer, and the thing that makes you look like the agency that actually manages deliverability instead of the one that just fires campaigns. The Agency tier produces these branded reports so the client sees your name, not a tool's.
Onboarding a new client: run the free check on their sending domain, fix the failing records with them, and confirm the domain is inbox-ready before the first campaign. Ongoing: add the domain to daily monitoring, and when an alert fires, fix it and send the client a short note with the branded report. When a client asks "are we still delivering?", you answer with a current score and a dated report, not a guess. That is the operational edge, and it compounds into retainers and referrals because you are the agency that never has a deliverability incident.
Run a free check on one of your client domains right now and see the seven-check score and the exact fixes: cold email deliverability checker. When you are ready to monitor the whole book and hand over branded reports, that is what the Agency tier is for.
For the full playbook across every client domain, see email deliverability for agencies and developers.