Cold email domain generator and fleet planner
Generate sending domains for cold outreach, check which ones are actually registrable, and build a fleet that does not share one obvious naming pattern. Every other generator in this category hands you variations of a single stem. That is the arrangement that took 11 of our own 16 sending domains offline at once.
Advanced controls
Generated names are already filtered for the things that score badly, so most of them land high and the score is there to rank within a good set. To see the full range, score a domain you already own below.
Score a domain you already own
Paste a sending domain you already use, or one you are about to buy elsewhere, and see it against the same census. This is where the full range of the score shows up.
How many sending domains do you need?
Domain count is a consequence of volume, per-mailbox sending rate and how many mailboxes you put on a domain. The rates below are what ReplyLead actually runs, not provider maximums. For the volume question itself see how many cold emails per day.
Why a separate domain, and why not variations of it
Your primary domain never sends cold email. That rule has no exceptions. Cold outreach carries bounce risk, complaint risk and listing risk, and if the domain your business runs on absorbs that, you lose the mail the business depends on: invoices, support threads, password resets, replies from customers.
Almost everyone gets that far. The part that gets skipped is what the secondary domains are called. The standard advice, and the output of every other generator in this category, is variations on one stem: getbrand.com, brandmail.com, brandhq.com, try-brand.com. Tidy, easy to manage, and instantly recognisable as a pattern, which is exactly the problem: a pattern legible to you is legible to a filter.
This is one incident on a 16-domain set, observed once. It is a reason to avoid a legible pattern; it is not a measured industry-wide rate, and we do not present it as one.
The rule we run on now: if you can describe your domain set in one sentence, so can a filter. Vary the stem, not just the suffix, and vary it across provider pools too, so that a Google-pool pattern and a Microsoft-pool pattern do not share a signature. That is what the generator above is built to do, and what the fleet analysis measures. The wider architecture, including provider mix and pool isolation, is covered in cold email infrastructure.
What 12.9 million business domains actually look like
The suitability score on this page is not a taste judgement. It is calibrated against a census of 12,915,691 business domains observed in ReplyLead contact data, each one resolved in DNS. Published here because we could not find this measured anywhere else, and because a generator that tells you a name is "too long" should be able to say what it is long compared to.
Shape of a real business domain
| Measure | Value | Read as |
|---|---|---|
| Median name length | 11 characters | Excluding the ending. Half of all business domains are shorter than this. |
| Middle half of the population | 8 to 15 characters | 25th to 75th percentile. |
| 90th percentile | 19 characters | Only one domain in ten is longer. |
| Contain a hyphen | 7.31% | 944,338 domains. |
| Contain two or more hyphens | 0.42% | 54,594 domains. Genuinely rare. |
| Contain a digit | 3.00% | 387,718 domains. |
| End in .com | 65.82% | Across 3,463 distinct endings in total. |
Naming structure and domains that stopped resolving
Every domain in the census was collected because it belonged to a real business at the time it entered our contact data. Some no longer resolve in DNS at all, which means the registration lapsed or was abandoned. Cross-tabulating that against name structure produces the finding below, on a reliably-resolved subset of 12,335,726 domains where the baseline no-longer-resolves rate is 9.26%.
| Name feature | Domains | No longer resolves | Against baseline |
|---|---|---|---|
| No hyphen | 11,420,028 | 9.20% | 0.99x |
| Exactly one hyphen | 863,227 | 9.66% | 1.04x |
| Two or more hyphens | 52,471 | 16.21% | 1.75x |
| No digit | 11,966,124 | 9.19% | 0.99x |
| Contains a digit | 369,602 | 11.64% | 1.26x |
| 6 characters or fewer | 1,615,038 | 6.42% | 0.69x |
| 7 to 9 characters | 2,641,476 | 7.98% | 0.86x |
| 10 to 12 characters | 2,909,499 | 9.22% | 1.00x |
| 13 to 15 characters | 2,401,924 | 9.96% | 1.08x |
| 16 to 18 characters | 1,542,155 | 10.77% | 1.16x |
| 19 to 22 characters | 911,599 | 12.04% | 1.30x |
| 23 characters or more | 314,035 | 14.26% | 1.54x |
The result worth keeping. One hyphen is close to neutral, at 1.04x the baseline. Two or more is not, at 1.75x. The same shape holds for length: the association is monotonic across every band, from 6.42% at six characters or fewer up to 14.26% at twenty-three or more. A digit sits at 1.26x. So the common advice to avoid hyphens entirely is, on this population, slightly overstated for a single hyphen and clearly understated for two.
Limitations, stated plainly
- This is observational and confounded. Domains entered the dataset at different times, so a longer observation window is one plausible driver of a higher lapse rate. Nothing here establishes that a naming choice causes abandonment.
- "No longer resolves" means NXDOMAIN in DNS. It is a proxy for a lapsed or abandoned registration. It is not a measure of spam, of blocklisting, or of deliverability.
- The population is business domains observed in ReplyLead contact data. It is not a random sample of the global DNS, and it is weighted toward the markets we sell into.
- One further census bucket, covering domains recorded as publishing no usable records, was excluded from the cross-tabulation: when we re-resolved a sample of it live, only 25.8% still matched. Excluding it is why the cross-tab denominator is 12,335,726 rather than the full 12,915,691.
- Structural measures such as length, hyphens and digits are properties of the name itself and do not go stale. Only the resolution state does.
How current this is
On 30 August 2026 we re-resolved a fresh sample of 1,600 domains against live DNS to measure how well the stored census still holds. Domains recorded as no longer resolving were confirmed at 98.0% (392 of 400). Domains recorded as having a working mail record were confirmed at 99.2% (397 of 400). The bucket that failed re-verification is the one excluded above.
https://replylead.com/cold-email-domain-generator.html#researchQuote the figures with their denominator and date attached. If you need a clarification or believe a figure is wrong, our correction process is on editorial standards.
Methodology
What availability means here
Registration status comes from RDAP, the Registration Data Access Protocol that replaced WHOIS. The tool reads the IANA bootstrap registry to find the authoritative RDAP server for each ending, then queries it directly from your browser. A 404 means the registry holds no record, so the name is available. A 200 means it is registered. A rate limit, a timeout, a server error or a missing RDAP service is reported as could not verify, and never as available. Checks run at bounded concurrency with pacing between requests, and results are cached for the session so repeat views do not re-query the registries.
Availability is a point-in-time reading and domains are registered continuously, so re-check at the registrar before buying. The IANA bootstrap currently lists RDAP servers for about 1,200 endings. Several popular ones, including .co, .us and .me, publish no public RDAP service, so this tool cannot verify them. It says so rather than guessing.
What outbound suitability scores, and what it does not
Outbound suitability is a naming and infrastructure heuristic. It does not predict inbox placement. No property of a domain name determines whether mail is delivered; authentication, sender reputation, list quality, volume and content do that. The score weighs eight things: length against the census percentile, hyphen count, digit presence, readability, spelling and dictation risk, whether the name reads as a legitimate business rather than a disposable one, how far it sits from your primary brand in both directions, and its registration state. Three of those weights, the length curve, the hyphen penalty and the digit penalty, are set from the census figures above rather than chosen by feel.
How fleet similarity is calculated
For the set you select, the tool computes pairwise character-bigram similarity across every pair, the longest shared prefix and suffix, the number of domains sharing a common word token, and the share of the set sitting on a single ending. The headline diversity score combines those into one number where high is good. It is transparent lexical analysis on the names alone. It has no access to registration dates, registrars, hosting or reputation data, and it makes no claim that a given score produces a given delivery outcome.
Where the capacity numbers come from
The planner uses ReplyLead's current operating rates, measured across our own live mailboxes: roughly 10 to 12 cold sends per Google Workspace mailbox per day and roughly 1 to 2 per Microsoft 365 (Exchange Online) mailbox per day, with 1 to 3 mailboxes per domain in the Google pool. These are operating choices, not provider ceilings. Google's own documented limit for paid editions is 3,000 external recipients per user per day, which is far above anything appropriate for cold outreach, and a technical ceiling is never a volume recommendation. Plan on two to three weeks of warmup per mailbox before real campaign volume. Warmup itself is covered on email warmup.
What the generator will not produce
No homoglyph or lookalike substitutions, no deliberate misspellings of your brand or anyone else's, and no names constructed to make a recipient believe the mail came from a different company. Brand-adjacent naming is legitimate and is offered as one family among six. Impersonation is not, and no setting turns it on. The tool does not screen for trademarks; that is a check to run with counsel before you register anything.
Privacy
Generation and scoring run entirely in your browser. Nothing you type is sent to a ReplyLead server, and there is no signup. The only outbound requests are the RDAP registration lookups, which go directly from your browser to the relevant domain registry.
Questions people actually ask
What is a cold email sending domain?
A sending domain is a separate domain, bought specifically for outbound email, that carries cold campaigns instead of the domain your business runs on. It exists so that bounces, complaints and any blocklisting land somewhere that is not your primary domain. Your primary domain never sends cold email.
How many sending domains do I need?
It follows from volume. At roughly 10 to 12 cold sends per Google Workspace mailbox per day with two mailboxes per domain, about 1,000 cold emails a month needs roughly 4 to 5 mailboxes across 2 to 3 domains. The planner above does the arithmetic for your number and provider mix.
Should my sending domains be variations of my main domain?
No. Variations of one stem share an obvious pattern, and blocklisting acts on patterns. We had 11 of our 16 sending domains listed at once because every one of them was built on the same brand word. Vary the stem itself, not just the prefix or suffix.
Is .com necessary for cold email?
It is not necessary, and 34% of the business domains in our census do not use it. What matters more is that the ending reads as ordinary to a human recipient and that your set is not concentrated on one unusual ending. The fleet analysis flags concentration on a single ending.
Why does the tool say "could not verify" on some domains?
Because the registry for that ending publishes no public RDAP service, or because the lookup was rate limited or timed out. An unverified result is never presented as available. Check those at a registrar before buying.
Does a domain name affect deliverability?
Not on its own. Authentication, sender reputation, list quality, volume and content determine placement. What the name affects is whether a set of domains is recognisable as a set, and whether it reads as a real business to a person. Once the domains exist, authenticate every one of them: the SPF and DMARC generator builds the records.
Next steps once the domains exist
Generate SPF and DMARC records for each new domain // Cold email infrastructure, the pool architecture these domains sit in // Email warmup before real volume // How many cold emails per day // Mail provider lookup // Cold email deliverability // Deliverability checker // All complimentary tools
Built and methodology reviewed by Mark Glazer, founder of ReplyLead. Census and tool last updated 30 August 2026. Our standards for what we publish and how to request a correction are on editorial standards.