# Sending to Outlook and Microsoft 365 {#sending-to-outlook-and-microsoft-365}


Microsoft checks authentication, sender reputation, content and links. Passing
authentication is required for reliable sending, but does not guarantee Inbox
placement. A delivery event means the receiving server accepted the email; it
does not tell you which folder received it.


## Authenticate the provider that sends your mail {#authenticate-the-provider-that-sends-your-mail}


For domains sending more than 5,000 messages a day to Microsoft's consumer
services, Outlook.com, Hotmail and Live, Microsoft requires SPF and DKIM to pass,
plus DMARC with at least `p=none`. The visible From domain must align with the
SPF or DKIM domain. This consumer threshold is distinct from Microsoft 365's
rules for mail sent to business tenants. Use all three protections at any volume.

Add the exact records shown in **Settings → Domains**. For a Nitrosend address,
Nitrosend manages the platform domain's records. With your own domain or a BYO
provider, publish and maintain the records supplied for that sending provider.
Do not add Microsoft's SPF include just because your recipients use Outlook.
Keep one SPF record per domain and account for its DNS lookup limit.

A dedicated sending subdomain helps separate configuration and mail streams.
It does not guarantee that reputation problems cannot affect the parent domain
or related senders. The technical sending domain and visible From domain may
differ when correctly verified and aligned. See [Sending domains](https://docs.nitrosend.com/guides/sending-domains.md).

Use an accurate sender name and a working From or Reply-To mailbox that your
team monitors. Subjects, links and sender details must represent the business
and message honestly.


## Send marketing to people who asked for it {#send-marketing-to-people-who-asked-for-it}


Follow the [Nitrosend terms](https://nitrosend.com/terms#acceptable-use): no
purchased, rented, scraped or harvested lists, impersonation, phishing or
deceptive messages. Keep records of where and when recipients agreed to receive
your marketing. Importing an address or seeing **Subscribed** in Nitrosend is
not evidence that the recipient gave permission.

Carry over unsubscribes and delivery suppressions when migrating an audience.
Do not work around them by importing again, changing an address or switching
brands, accounts or providers. See [Managing contacts](https://docs.nitrosend.com/guides/managing-contacts.md).


## Make unsubscribing easy {#make-unsubscribing-easy}


Marketing email needs a visible, working unsubscribe link and the sender's
required postal details. Nitrosend's campaign and marketing-flow paths include
the compliance footer and the `List-Unsubscribe` and `List-Unsubscribe-Post`
headers used for one-click unsubscribe. Keep these in the final email when
using a custom footer or BYO provider.

The footer link opens a confirmation page. A recipient's email app can also
submit the one-click request directly, without a Nitrosend login. Nitrosend
applies that unsubscribe to the contact's email marketing for the sending brand.
It keeps the contact record; another brand's subscription is separate. Process
opt-out requests received by reply too, promptly and within applicable legal
and mailbox-provider deadlines.

Hard bounces and complaints have separate delivery protections and can also
prevent transactional sends. Transactional messages are for requested or
necessary service communications; do not label a promotion transactional to
avoid an unsubscribe.

Test sends use a preview unsubscribe link and omit the live marketing
unsubscribe headers. They are useful delivery checks, but do not prove that a
live campaign's unsubscribe works or that every recipient will reach Inbox.


## Handle bounces and complaints {#handle-bounces-and-complaints}


Stop sending to addresses with hard bounces or complaints. Investigate repeated
temporary failures and remove invalid addresses from your next audience. Do
not keep resubmitting a message Microsoft permanently rejected with a `5xx`
response. A sender authentication or policy error needs a sender correction;
it does not by itself prove that the recipient address is invalid.

Nitrosend records provider feedback and checks applicable suppressions before
sending. With BYO, configure the provider's feedback connection as described
in its integration guide. A provider that never reports outcomes cannot give
Nitrosend a complete bounce or complaint history.

The sending provider owns the outbound server's reverse DNS, transport security
and SMTP behaviour. With BYO, confirm these with that provider. A connected
Microsoft 365 mailbox is also subject to Microsoft's mailbox sending limits;
Microsoft does not support Exchange Online as a bulk-marketing delivery service.


## Investigate the actual delivery result {#investigate-the-actual-delivery-result}


- **Rejected:** keep the full SMTP response, time, sender, recipient and message
  ID. Correct the reported problem before another send. Microsoft's delisting
  portal is for the block codes it identifies, rather than every Junk result.
- **Accepted into Junk:** ask the recipient's Microsoft 365 administrator to
  inspect the message in Defender's Email entity page. Compare the original
  and latest verdict, delivery location, detection technology, policy overrides,
  timeline and URL verdicts. Check the message's bulk complaint level against
  the effective anti-spam policy; authentication alone does not explain it.
- **Link warning:** inspect the exact link and its redirect destinations
  separately from the sender verdict. Report a legitimate link or message to
  Microsoft as a false positive. A clean review does not guarantee later Inbox
  placement or recovery in every tenant.

SNDS provides data about sending IPs you control, and JMRP supplies Outlook.com
complaint feedback. Shared-provider IPs belong to that provider; ask it to
investigate. There is no public check that proves an entire domain is clear of
all Microsoft filtering. Allow-listing a test sender does not establish that
delivery to customers has recovered.

Report unwanted or deceptive Nitrosend mail to
[contact@nitrosend.com](mailto:contact@nitrosend.com). Include the original
message or full headers and explain the problem. For a delivery investigation,
include an affected message ID and the recipient provider's diagnostic result.


## Microsoft's published guidance {#microsofts-published-guidance}


- [Outlook.com high-volume sender requirements](https://techcommunity.microsoft.com/blog/microsoftdefenderforoffice365blog/strengthening-email-ecosystem-outlook%E2%80%99s-new-requirements-for-high%E2%80%90volume-senders/4399730)
- [Microsoft 365 external sender policies](https://learn.microsoft.com/en-us/defender-office-365/external-senders-policies-practices-guidelines)
- [Microsoft anti-spam header definitions](https://learn.microsoft.com/en-us/defender-office-365/message-headers-eop-mdo)
- [Microsoft 365 bulk-mail handling](https://learn.microsoft.com/en-us/defender-office-365/anti-spam-bulk-complaint-level-bcl-about)
- [Microsoft 365 outbound spam and bulk-mail guidance](https://learn.microsoft.com/en-us/defender-office-365/outbound-spam-protection-about)
- [Microsoft 365 blocked-IP delisting](https://learn.microsoft.com/en-us/defender-office-365/external-senders-use-the-delist-portal-to-unblock-yourself)
- [Outlook.com Postmaster](https://substrate.office.com/ip-domain-management-snds/postmaster)