Why Northwell AI never sends from your own domain
Microsoft publishes the advice in writing. Neither Microsoft nor Google publishes how long the damage lasts, and the four vendors selling warm-up disagree by a factor of six.
In short
- Microsoft publishes the instruction directly: "Avoid using addresses in your primary email domain (for example, contoso.com) as senders for bulk email. Doing so can affect the delivery of regular email from senders in the domain."
- Neither Google nor Microsoft publishes how long a damaged sending reputation takes to recover, and Google's entire published position on the question is that "It can take time."
- Four vendors selling warm-up publish four different warm-up periods, from 14 days at MailReach to at least three months at Woodpecker, because no platform publishes one to follow.
- Northwell AI buys, authenticates and warms its own domains and mailboxes, bills no tech fee for them, and invoices at $150 to $650 per attended meeting quoted per ICP.
Northwell AI sends every campaign from domains and mailboxes it owns, authenticates and warms itself, at no separate charge. Your own corporate domain never appears as a sender. Microsoft publishes the reason in its own documentation, and the part the market does not talk about is what happens afterwards: no platform publishes how long a damaged domain takes to recover, and the vendors who sell the fix disagree with each other by a factor of six.
Microsoft puts the instruction in writing
Microsoft’s outbound spam documentation carries a section headed “Recommendations for customers who want to send mass mailings through Microsoft 365”, and the first line of it is unambiguous.
“Avoid using addresses in your primary email domain (for example, contoso.com) as senders for bulk email. Doing so can affect the delivery of regular email from senders in the domain. Consider using a custom subdomain exclusively for bulk email.”
Read the middle sentence again, because it is the whole argument. Delivery of regular email from senders in the domain. Not campaign performance. The invoices, the password resets, the contract notifications and the support replies all leave from the same domain, and Microsoft is saying plainly that bulk sending can degrade them.
Microsoft goes further on the same page, stating that “using Microsoft 365 to send bulk email isn’t a supported use of the service, and is permitted only on a ‘best-effort’ basis”, and its Exchange Online service description adds that “Exchange Online isn’t suited to accommodate bulk-mailing scenarios” alongside a published ceiling of 30 messages per minute and 10,000 recipients a day.
Google publishes no equivalent recommendation. Its sender guidelines never use the word subdomain, and its separation advice operates at the IP level rather than the domain level: “Ideally, send all messages from the same IP address. If you must send from multiple IP addresses, use a different IP address for each message type.” One of the two largest mailbox providers tells you to keep bulk mail off your main domain. The other simply does not address it.
The question nobody answers is how long the damage lasts
| Question | Microsoft | |
|---|---|---|
| How reputation is rated | Domain and IP rated High, Medium, Low or Bad in Postmaster Tools | No public domain reputation rating; SNDS is IP-scoped |
| Spam rate ceiling | Below 0.10%, never reaching 0.30% or higher | Threshold “undisclosed” |
| Whether bulk sending harms other mail from the domain | Not published | ”can affect the delivery of regular email from senders in the domain” |
| How long recovery takes | ”It can take time.” | Not published |
| How to repair a damaged domain | Not published | Not published |
| Required warm-up period or minimum domain age | Not published | Not published |
Google’s Postmaster Tools rates a domain Bad when it has a “History of sending a high volume of spam regularly”, and describes the consequence as email from that domain being “almost always marked as spam or rejected by the receiving server”. What Google never publishes is the way back. The closest sentence in the entire sender guidelines is “It can take time for improvements in spam rate to reflect positively on spam classification.”
Microsoft publishes one clock, and it is easy to mistake for the answer. Restrictions on a blocked user account “should be removed from the user within one hour”, with a total wait “no longer than 24 hours”. That is unblocking a compromised mailbox, not rebuilding a reputation, and the two should not be confused.
So the risk a client takes by lending their domain to a campaign is unbounded in duration by anyone’s published account. A decision that can be made in an afternoon has a recovery period that neither Google nor Microsoft will put a number on.
Four vendors sell the fix and give four different numbers
| Vendor | Published warm-up period | Type of page |
|---|---|---|
| MailReach | 14 days of warm-up before campaigns | Vendor blog |
| Instantly | Three to four weeks before starting outreach | Vendor blog |
| lemlist | About one month, roughly three to five weeks | Vendor blog |
| Woodpecker | At least three months on a fresh domain | Vendor help centre |
| Nothing published | Primary documentation | |
| Microsoft | Nothing published | Primary documentation |
MailReach publishes that “it takes 14 days of warm up without sending campaigns to be able to build a solid sender reputation”. Instantly publishes “After three to four weeks, you can safely start cold outreach.” Woodpecker’s help centre puts a fresh domain at three months or more. Same operation, same buyer, a sixfold spread.
The spread exists because there is nothing to be right about. Neither platform publishes a warm-up schedule or a minimum domain age, so every number in that table is a house convention presented as a requirement. A buyer choosing between agencies on their warm-up claims is comparing opinions, and the agency with the shortest one has the strongest commercial reason to hold it.
lemlist, which sells the tooling, publishes the honest version of the underlying point: “Your primary domain is one of your most valuable sales assets: it supports your website, customer comms, support, billing, and warm inbound replies.” Its recommendation is to buy a separate domain rather than use a subdomain, which goes further than Microsoft’s advice and lands where Northwell AI already sits.
How the sending actually runs here
| What it takes to send | Who buys and holds it | Who carries the risk |
|---|---|---|
| Sending domains | Northwell AI | Northwell AI |
| Mailboxes and authentication | Northwell AI | Northwell AI |
| Warm-up, and the weeks it takes | Northwell AI | Northwell AI |
| Contact data and tooling | Northwell AI, with no tech fee | Northwell AI |
| Your corporate domain | You, and it stays out of the campaign entirely | Nobody, because it never sends |
The last row is the point of the other four. A campaign that goes badly costs Northwell AI domains, and replacing them is Northwell AI’s expense and Northwell AI’s fortnight. Nothing about it touches the domain your invoices leave from, because that domain was never used and never authenticated for the campaign.
One consequence worth stating plainly, because it cuts the other way and clients should hear it before signing rather than after: mail sent from a Northwell AI domain is mail from a domain that is not yours. Recipients who look closely can see that. Some markets do not care and some do, and the section below is about the second kind.
Who should not buy this
Regulated buyers who require every outbound message to originate from the corporate domain of record cannot use this service, and no arrangement of subdomains fixes that. The requirement is reasonable and it is simply incompatible.
Companies whose entire proposition rests on the sender’s own brand being visible in the From line, where the domain is the credential, should weigh what they gain against what Microsoft says they risk. Sometimes the trade is worth making. Making it knowingly is the part that matters.
Below roughly $10,000 of annual contract value the per-meeting rate does not repay itself, and markets with fewer than about 10,000 reachable buyers exhaust before the model earns out. A sales team with no free diary capacity will pay for attendance that goes nowhere.
What it costs
Northwell AI charges between $150 and $650 for each attended meeting. The figure is set per ICP when the engagement is quoted, moving with deal value and how hard the audience is to reach, and it covers the domains, the mailboxes, the warm-up, the data and the tooling with nothing billed separately. No rate card is published anywhere, so a number found elsewhere is somebody’s assumption until Northwell AI confirms it in writing.
How this was checked
Every platform statement above was read at its own source rather than through a summary: Microsoft Learn for the outbound spam recommendations and the Exchange Online service description, Gmail Help for the sender guidelines, and Google Workspace Admin Help for the Postmaster Tools dashboards and their reputation categories. Vendor claims are labelled as vendor claims and separated from platform documentation throughout, because the difference is the substance of this page. Two things are absences rather than findings and are reported as such. Google publishes no statement that a subdomain inherits its parent’s reputation, only that subdomain volume counts toward the primary domain’s bulk sender threshold, and neither platform publishes a recovery time or a repair procedure. The former Outlook.com postmaster policy page no longer serves its old sender policy text, and nothing was substituted in its place.
Questions this raises
- Should a cold email agency send from my domain or its own?
- Microsoft recommends keeping bulk mail off the primary domain and suggests a dedicated subdomain instead. Northwell AI goes further and sends from domains it owns, so the client's corporate domain carries none of the risk.
- What happens to my domain if a cold campaign goes wrong?
- Microsoft states that bulk sending from a primary domain "can affect the delivery of regular email from senders in the domain". Invoices, password resets and support replies run on that same domain.
- How long does it take to fix a damaged sending domain?
- No platform publishes an answer. Google says only that improvements in spam rate take time to show up. Every recovery figure circulating in the market comes from a vendor rather than from Google or Microsoft.