Why cold email breaks quietly
Cold outreach runs on volume spread thin. A typical agency setup has several secondary domains per client, two or three mailboxes per domain, and a sending tool that rotates between them. Each domain sends a modest number of messages a day, which keeps it under the radar, but also means nobody looks at any single domain closely.
When one domain lands on Spamhaus DBL or URIBL, its replies stop and the sending tool keeps using it. When a DNS change drops a DKIM record, every mailbox on that domain starts failing DMARC. Reply rates fall a little, the client notices a week later, and by then the domain has spent days hurting its reputation. Cold email needs monitoring that looks at every domain, every few minutes, and speaks up the moment one changes.
What we monitor for each sending domain
- Domain blacklists. Spamhaus DBL, SURBL, URIBL and other domain lists, which matter most for cold email because they judge the domain in your From address and links.
- IP blacklists for the mailbox provider or SMTP servers you send through, including Spamhaus ZEN, Barracuda and SpamCop.
- SPF, including the 10 DNS lookup limit that is easy to break when you stack a workspace provider and a sending tool.
- DKIM on the selectors your provider uses, and DMARC with a policy and rua address.
- MX and the root domain redirect, so a domain does not look abandoned to a curious prospect or a filter.
- Inbox placement per provider with seed tests, so you see Gmail and Outlook treat each domain differently.
How a cold email agency uses alerts
Our guide to cold email domain rotation covers how to keep spare domains warm, how many mailboxes to run per domain, and when to retire one.
- 1 Import all client domains in bulk and tag them by client and by sending tool.
- 2 Route alerts for each client to its own Slack channel, or to one channel for the deliverability lead.
- 3 When a domain gets listed, pause its mailboxes in the sending tool and check what changed: copy, list source, volume.
- 4 Follow the removal steps from the alert for that list, then wait for the delisting alert before you resume.
- 5 If a domain gets listed again soon after removal, retire it and move volume to a warmed spare.
Run a free check on your own domain or IP, then keep it monitored.
Check NowThe rules cold senders cannot ignore
Google and Yahoo apply their February 2024 rules to bulk senders, but the basics apply to everyone: SPF and DKIM must pass, a DMARC record should exist, and the user-reported spam rate must stay under 0.3 percent, ideally under 0.1 percent. Cold email is the category most likely to collect spam reports, so a domain with a few dozen complaints in a day can cross that line on its own. Microsoft added authentication requirements for high volume senders to Outlook.com in May 2025, and filters at both providers act on domain reputation quickly.
Each sending domain also needs a working PTR on the sending IP, which your mailbox provider handles, and a custom tracking domain if your tool rewrites links, so you do not share a link domain that another sender got blacklisted.
Why weekly checks are not enough
Some cold email tools run automated blacklist checks once a week. A domain listed on Monday can send five days of campaigns into spam before the next check. At 5-minute intervals, you see the listing during the same sending window and can pause before most of the day's volume goes out.
Checks are DNS lookups only. We never send from your domains or log in to your mailboxes, so monitoring adds nothing to your sending footprint. For a one-off look at a domain you are about to buy or reuse, use the free domain blacklist check.
Plans that fit cold email volume
Agency adds client workspaces, tags, bulk import and white label deliverability reports, so each client sees the health of their own domains under your brand. Monthly prices are $149, $499 and $1,499.
| Plan | Domains and IPs | Interval | Inbox tests per month | Billed yearly, per month |
|---|---|---|---|---|
| Business | 100 | 15 minutes | 50 | $74 |
| Agency | 500 | 5 minutes | 300 | $249 |
| Scale | 5,000 | 5 minutes | 1,500 | $749 |
Frequently asked questions
How do I monitor deliverability across many cold email domains?
Import every sending domain into one monitoring workspace, check blacklists and authentication every few minutes, and route alerts to Slack. Add inbox placement tests per domain to catch reputation drops that no blacklist shows.
Which blacklists matter most for cold email?
Domain lists such as Spamhaus DBL, URIBL and SURBL, because cold email usually goes through large mailbox providers whose IPs rarely get listed, while your own domains and links carry the risk.
How many cold emails can I send per mailbox per day?
Most agencies keep each mailbox between 30 and 50 cold emails a day after warm-up, and spread volume across several domains rather than pushing one harder.
Should cold email domains have DMARC?
Yes. Google and Yahoo expect a DMARC record, and a domain without one looks less trustworthy to filters. Start with p=none and a rua address so you can see what sends as the domain.
What should I do when a cold email domain is blacklisted?
Pause its mailboxes, find and fix the cause (list quality, copy, volume), request removal, and only resume after the listing clears. A domain that keeps getting relisted should be retired.