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
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.
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
Follow the Nitrosend terms: 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.
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
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
- 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. 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.