Email Domains: Types, DNS Records, Outreach

What is an email domain, and how is it different from an email address?

An email address has two parts on either side of the @. The local part (name) picks out one mailbox. The domain (example.com) says which organisation's mail servers handle that mailbox. So one domain can hold thousands of addresses, while an address only ever belongs to one domain. The domain is also the thing other servers check. A receiving server looks up the domain's DNS to find out where to deliver mail (MX records) and whether a sender may send in its name (SPF, DKIM and DMARC records). That's why the domain carries the sender reputation and a single address doesn't. A website domain and an email domain can be the same name and still run on different services. The web host serves example.com over HTTP, and a separate mailbox host takes mail for it because its MX records point there. If you move your website, your mail keeps working, as long as nobody touches the MX records.

Which types of email domains are there?

Most domains you'll see in a contact list fall into one of four groups. What separates them for a sender is who controls the DNS, because that decides who can authenticate mail sent from the domain.

Type	Examples	Who controls the DNS	Use in B2B outreach
Free webmail	gmail.com, outlook.com, yahoo.com	The provider	You can't add DKIM for a third-party sender, so mail sent through a sending service with a gmail.com From address can't align under DMARC
ISP and regional providers	comcast.net, web.de, qq.com	The provider	Same limit as free webmail. Usually personal addresses, not company inboxes
Custom business domain	yourcompany.com, a subdomain like mail.yourcompany.com	You, through your registrar or DNS host	The only type where you can publish SPF, DKIM and DMARC for the services you send with
Disposable domains	Throwaway inbox services	The service	Addresses expire. They show up in sign-up lists and are worth filtering out before an import

What are the most common email domains?

Most common-domain lists are led by the big free webmail domains. One page in Google's results for this search, dated February 2020, gives gmail.com 18%, yahoo.com 17% and hotmail.com 16%. That's an old snapshot, and the page doesn't say how it was measured, so read it as a ranking and don't rely on the shares. Alternative providers add a long tail. According to mail.com's own domains page, cited in Google's AI overview, mail.com offers over 100 domain choices such as engineer.com and consultant.com. For an outreach list this matters for a practical reason. A freemail address on a B2B list is usually someone's private inbox, not a company mailbox. Under EU rules, consent and legitimate-interest questions depend on whose data it is, so a lot of senders sort freemail domains into a separate segment before they decide whether to contact them at all. For that sorting, the domain is the only signal you have.

How do I check if a domain is available?

1. 1 Search the name at any domain registrar. The search queries the registry for the top-level domain (.com, .de, .io) and says whether it's registered.
2. 2 If it's taken, look it up via RDAP or WHOIS. ICANN's registration data lookup shows the registrar and the creation and expiry dates, which tells you whether the name might lapse.
3. 3 Check whether a registered domain already handles mail: run dig MX example.com. If MX records come back, the domain receives mail somewhere, so buying it later means inheriting whatever reputation it built up.
4. 4 Check its history before you send from it. Run the domain through blocklist lookups, because a previously used domain can still be listed under its past owner's behaviour.

An expired domain that used to send mail isn't a clean start. Receiving servers rate the domain, not the owner, so its old reputation comes with it.

How do you set up a custom email domain?

First you register the domain. Then you pick a mailbox host and publish its MX records, so mail for the domain reaches its servers. For a mailbox, the realistic options are the hosts below. Each of them supports custom domains and gives you the DNS records to publish (Zoho, Proton and mailbox.org describe this on their custom-domain pages, which Google's AI overview cites).

Host	What it is	Suits	Where it stops
Google Workspace	Mailbox and office suite with the Gmail interface	Teams that already work in Gmail and Google Docs	A mailbox host, not a bulk sender. Per-user sending limits apply
Microsoft Exchange Online	Microsoft's business mailboxes, used with Outlook	Organisations on Outlook, Teams and Windows	Also a mailbox host, with per-mailbox sending limits
Zoho Mail	Standalone business mailbox host	Small teams that want mail without a full office suite	Fewer integrations than the two large suites
Proton Mail	Swiss-based host focused on encryption	Teams that put end-to-end encryption first	Encryption features apply mainly between Proton users
mailbox.org	Berlin-based mailbox host	Teams that want a host operating under German law	A smaller ecosystem of add-on tools

A mailbox host and a sending service are two separate jobs. If you also send campaigns or outreach through Brevo, the domain needs Brevo's DKIM record as well as the mailbox host's, plus an SPF record that covers both. The SPF part is explained in DKIM DMARC and SPF for cold email senders.

Which DNS records does an email domain need?

Record	Where it lives	What it does	Common failure
MX	The domain itself	Names the servers that accept mail for the domain	Old MX records left in place after a host move split incoming mail
SPF (TXT)	The domain itself, one record only	Lists the servers allowed to send for the domain	Two separate SPF records, or so many nested includes that the record exceeds the DNS lookup cap in the SPF standard, which makes the check fail with an error
DKIM (TXT or CNAME)	selector._domainkey.example.com	Publishes the public key that verifies a message's signature	The sending service signs with its own domain, so DKIM doesn't align with your From domain
DMARC (TXT)	_dmarc.example.com	Says what to do when neither SPF nor DKIM aligns, and where to send reports	A policy of p=reject published before every sender is aligned

You can see what a domain publishes right now with the SPF DKIM DMARC checker. It reads the live DNS, so changes show up there once they've propagated.

Should cold outreach use your main domain or a separate one?

There are three setups, and each has a cost. Sending from your main domain puts its reputation at risk, and invoices and support mail ride on that same reputation. A subdomain such as outreach.example.com gets its own DKIM key and can have its own DMARC record. But receivers can still connect it to the parent domain, so it softens the risk without removing it. A separate lookalike domain keeps the main domain out of it, but it starts with no reputation, needs its own full set of SPF, DKIM and DMARC records, and has to be warmed up. Here's what doesn't work. Sending outreach through a third-party service with a gmail.com or outlook.com From address can't pass aligned DMARC, because you can't publish a DKIM key in a domain you don't own. A brand-new domain sending at full volume on day one doesn't work either. Ramp-up is covered in email warm up: daily volumes and DNS setup.

How EmailFlow OS uses your own sending domain

EmailFlow OS, a EmailFlow OS product, sends video email from the customer's own domain rather than from a shared platform address. You record one video and upload it to EmailFlow OS. You connect your Brevo account and your sending domain, then import your prospect list into EmailFlow OS. EmailFlow OS turns that single recording into a separate personalised version for each recipient, not one per company. It sends each version from your own inbox, through your own Brevo account and your own sending domain. So the DNS records in the table above stay under your control, and so does the reputation they build. How the per-recipient video works is described on the EmailFlow OS personalised video email page.

Outreach questions that follow from the domain setup

Cold email deliverability

Cold email deliverability is decided by the receiving server. It weighs the sending domain's authentication (aligned SPF or DKIM under DMARC), the domain's reputation, bounces and complaints. You control the inputs: correct DNS records, a verified list and a steady volume. You don't control the outcome. What decides it is broken down in cold email deliverability: what decides it.

What is a good email deliverability rate?

The usual "deliverability rate" in sending dashboards is really a delivery rate: messages accepted by the receiving server, minus bounces. It says nothing about whether those messages landed in the inbox or the spam folder. Inbox placement only shows up in seed tests or provider data such as Google Postmaster Tools. So compare your delivery rate with your own past sends, not with a borrowed benchmark, and treat a sudden rise in hard bounces as a list problem.

Email prospecting

Email prospecting means finding the right person at a target company, verifying the address, and writing a first message that gives a specific reason for contacting them. The domain step comes in twice. The prospect's domain tells you whether you've got a company or a freemail address. Your own domain carries the send.

Sales follow up email template

A workable sales follow-up template: "Hi [first name], following up on my note from [day] about [specific problem]. Is [one-question ask] worth a short call, or should I check back next quarter?" One ask, one reference to the first email, and a simple way to say no. More versions by situation are in the sales follow up email template collection.

Follow up sales email

A follow-up sales email should reply inside the original thread, not start a new one. Mail clients group messages using the In-Reply-To and References headers. If you type "Re:" into a fresh subject line without those headers, the message looks like a reply but doesn't thread like one.

Questions people ask

? What are some email domains that start with the letter A?

Common ones are aol.com, the free webmail domain run by AOL, and att.net, AT&T's ISP domain in the US. Both are consumer domains whose DNS is controlled by the provider, not the user. In a B2B list they usually mean a personal inbox rather than a company mailbox, which is worth flagging before an import.

? Can I send business outreach from a gmail.com address?

You can send from it through Gmail itself. But if you send through an external service like Brevo with a gmail.com From address, you can't publish the DKIM key for gmail.com, because Google controls that DNS. DMARC alignment then fails. A custom domain is the only setup where you can authenticate each service you send through.

? Is a subdomain a separate email domain?

Technically yes. outreach.example.com has its own MX, SPF and DKIM records and can publish its own DMARC record at _dmarc.outreach.example.com. If it doesn't, the parent domain's DMARC policy applies. Receivers can still associate the subdomain with the parent, so it splits reputation only partly, unlike a separately registered domain.

? Does changing my email host change my email domain?

No. The domain stays registered with your registrar. Changing hosts means replacing the MX records, swapping the old host's SPF include and DKIM record for the new host's, and leaving DMARC in place. Addresses stay the same. Mail goes wrong mainly when old and new MX records are both published during the move.