Custom sending domains: setup, warmup, and multiple domains
By Clint ParsleyLast updated
In short. Add your domain under Settings → Sending, publish the DNS records, and verify. New domains warm up over at least 21 days (100, then 500, then 2,000 sends per day), and each step also waits until the domain has sent enough. Business verifies up to five domains, each with its own From name, and every campaign picks which one to send from.
A custom sending domain puts your own domain on platform sends (broadcasts and platform-routed mail) instead of the shared SEMAOS domain, so you build and own your sending reputation. Every paid tier includes at least one custom domain; Business verifies up to five. The Free tier sends only through your connected Gmail or Outlook mailbox, so it has no platform sending domain at all.
A trial can verify its own domain. Checking that mail from your domain reaches the inbox is the main reason to run a trial, and the trial's flat send cap limits the risk. Setup lives under Settings → Sending.
How do I set one up?
Add your domain and SEMAOS generates the DNS records to publish at your DNS host:
| Record | Where | What it does |
|---|---|---|
| TXT | _semaos.yourdomain.com | Proves your account controls the domain. The value is unique to your account, so the domain only verifies for you, even if someone else once set it up. |
| CNAME (several) | Under _domainkey.yourdomain.com | Publishes the keys for DKIM signing, the signature standard defined in RFC 6376 that lets a receiver check the mail really came from your domain. |
| MX and TXT | The custom MAIL FROM subdomain | Gives bounces a home on your domain and carries its SPF record, the setup Amazon SES documents in Using a custom MAIL FROM domain. |
Copy each record exactly (the page has one-click copy for each), publish them, then hit Check status. Verification usually completes within a few minutes of the records propagating, though DNS changes can occasionally take longer. Publish the ownership record at the same time as the others. SEMAOS looks for it once DKIM verifies, and DNS resolvers remember a record they looked for and did not find, often for up to an hour, so an ownership record added later can take that long to be seen. The badge shows the domain's status, and when only the ownership record is still missing, the page says so and opens the records list.
Two practical notes. First, publish the records at whatever DNS host serves your domain, which is not necessarily your registrar. Second, if your domain already sends email elsewhere, these records add to what's there; they don't replace your existing mail setup.
What is warmup, and why can't I skip it?
Inbox providers judge sending domains largely by history, and a brand-new domain has none. Google's sender guidelines say it directly: start with a low volume to engaged recipients, increase it slowly, and avoid sudden spikes. A domain that goes from zero to thousands of emails on day one matches the signature of a spammer on a fresh domain, so providers junk it preemptively. Warmup builds the history gradually: SEMAOS caps a new custom domain's daily platform sends, and the cap climbs through three steps over 21 days.
The step you're on is the more cautious of two things: how long the domain has been verified, and how much it has actually sent. Age alone doesn't clear it. A domain that was verified weeks ago but has barely sent stays at a lower step until its real volume catches up, because providers build a domain's reputation from the mail it sends, not from its age. Sends beyond a day's allowance aren't lost; they wait and go out the next day.
When volume is the thing holding you back rather than the calendar, the warmup banner says so and shows the count (for example, "400 of 700 sends to the next step"), so you can see how much more sending it takes to lift the cap. Once the domain has both aged past the schedule and sent enough to earn it, it sends at your plan's normal limits. The warmup schedule can't be adjusted, on purpose: a faster ramp would no longer look like warmup to inbox providers.
Does warmup affect my mailbox sends?
No. Warmup governs the platform channel only. Your connected Gmail or Outlook mailbox has its own established reputation and its own daily cap, so 1:1 and sequence sending continues at full speed while a new custom domain warms up. The exception is a sequence enrollment bigger than your mailbox's remaining daily budget, which moves to your custom domain and is capped by its warmup (see sending channels). Running both in parallel is the intended pattern for a new account: mailbox for outreach now, custom domain warming in the background for broadcasts later.
Can I send from more than one domain?
On Business, yes: verify up to five sending domains. Every other paid tier verifies one. Multiple domains are meant for teams that run more than one brand or region from a single account. Each domain warms up on its own 21-day clock, so verifying a second domain doesn't reset the first.
Each verified domain carries its own sender identity: a From name and a From address you set on the domain's card under Settings → Sending. Recipients of a send from that domain see that name, not your account default.
Every broadcast, one-off send, and sequence picks which verified From to send from. A sequence picks one From for all its steps, and any step can override it. If you don't pick one, a one-off or sequence send goes from your connected mailbox, or from your account default when no mailbox is connected; broadcasts always use your account default. Leave a domain's identity fields blank and it falls back to that default too, so you only fill them in for the brands that need a distinct name.
If you remove a domain, or downgrade below the number of domains you've verified, campaigns pinned to a domain you no longer have don't fail. They fall back to your default sending address so mail keeps going out. Set the domain you care about most as your default before a downgrade takes effect, and it's the one that's kept. When you remove a domain you no longer plan to use, delete its SEMAOS DNS records at your DNS host too.
What if another account already has my domain?
A domain belongs to one SEMAOS account at a time. If you add a domain that another account has listed, SEMAOS refuses it and shows a record under Prove you own a domain: a TXT record at _semaos.yourdomain.com with a value made for your account alone. Publish it at your DNS host, then press Check record. Checking needs a spare custom sending domain on your plan: if your domains are all in use, remove one first (or upgrade, if a larger plan has more).
SEMAOS looks for the record at your domain's own name servers and at a public DNS resolver. If both have it, the other account never finished setting the domain up, and nothing else stands in the way, SEMAOS moves the domain to your account and emails the other account. Reload Settings → Sending to finish setting it up; you get your own DNS records to publish. If the check asks you to try again, wait a minute and check once more; if it keeps failing for the same reason, the claim goes to support after a few tries.
If the other account added the domain in the last week and its DNS records already check out, it is told first. We email it the date the domain will move, 72 hours away, and you can see that date under Prove you own a domain. This needs a little over 4 days left on your record; check it later than that and the claim goes to support instead. It can keep the domain by publishing its own ownership record, which sends the claim to our support team, or by replying to that email so support can step in before the date. If neither happens, and nothing else changes on either account first, the domain moves to your account at or after that date and we email you. Keep your record published until then.
Other claims go to our support team instead, with the evidence. That happens, for example, when the other account verified the domain, when its own record is published too, when your record has only about 4 days left or less and the other account must be told first, when a third account also lists the domain, when the domain changed hands this way in the last 30 days, or when the check couldn't confirm your record everywhere it looked. While support reviews your case, the domain doesn't move to you on its own. Support emails you with the decision, so keep the record published until you hear back. If a domain was moved out of your account this way, reply to the email we sent you about it.
The record is valid for 7 days. If it expires before you check it, add the domain again for a new one. A claim already with support stays listed after its record expires; withdraw it first, then add the domain again. If the other account removes the domain in the meantime, just add it again: the record you already published counts for your new setup too. If support declines a claim, you can't open another one for that domain for a week, and any later claim from your account for that domain goes to support rather than moving on its own.
If your trial ends, or your account moves to the Free plan, while a claim is open, we close the claim and email you. Free does not include custom sending domains. After you upgrade, add the domain again to start a new claim.
When should I add a custom domain?
Before you need it, because of the 21-day clock. The product nudges you toward one after sustained platform sending on the shared domain, but the better move is starting verification the week you sign up if you know broadcasts are in your plans. A domain verified in week one is fully warmed by week four. If you're on Business and plan to run several brands, verify each one early for the same reason.