Outlook SMTP Settings: Server, Port and the 2026 Auth Change
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Here are the Outlook and Microsoft 365 SMTP settings for sending mail from an app. The server and port are straightforward. The thing you really need to know in 2026 is that Microsoft is retiring basic authentication for SMTP, so how you sign in matters more than it used to.
The short version
- Microsoft 365's SMTP server is smtp.office365.com; personal Outlook.com uses smtp-mail.outlook.com. Both on port 587 with STARTTLS.
- Your username is your full email address.
- Microsoft is retiring basic authentication (username and password) for SMTP through 2026. OAuth 2.0 is the replacement.
- Tools that connect over OAuth (you sign in through Microsoft's screen) keep working through the change.
- Microsoft 365 caps you at 10,000 recipients a day, so SMTP from one mailbox isn't built for cold outreach at scale.
The settings
| Setting | Microsoft 365 (business) | Outlook.com (personal) |
|---|---|---|
| SMTP server | smtp.office365.com |
smtp-mail.outlook.com |
| Port | 587 |
587 |
| Encryption | STARTTLS | STARTTLS |
| Username | your full email address | your full email address |
| Authentication | OAuth 2.0 (basic auth retiring) | OAuth 2.0 |
Port 587 with STARTTLS is the setting for both. Older guides mention port 25, but that’s blocked for normal sending.
The 2026 basic-authentication change
This is the important part. Basic authentication, signing in with just a username and password over SMTP, is being switched off. Microsoft has moved it to disabled-by-default through 2026, and new Microsoft 365 tenants won’t have it available at all. If a tool tries to log in with your Outlook password, it will eventually fail with an error like:
550 5.7.30 Basic authentication is not supported for Client Submission.
The replacement is OAuth 2.0: you sign in through Microsoft’s own login screen and grant the app permission, so no password is stored. This is more secure and it’s the direction everything is heading.
Microsoft 365 sending limits
For Microsoft 365 business accounts:
- 10,000 recipients per day.
- 500 recipients per single message.
- Around 30 messages per minute.
Personal Outlook.com is much lower, roughly 300 recipients a day. As always, these are technical ceilings, not sending targets. Pushing a single mailbox towards its limit with cold email invites reputation trouble.
Fixing common Outlook SMTP errors
- “550 5.7.30 Basic authentication is not supported”: basic auth is disabled for this tenant. Switch to a tool that connects over OAuth.
- “Authentication unsuccessful”: wrong credentials, or SMTP AUTH is disabled for the mailbox in the Microsoft 365 admin centre. Check both.
- Connection refused or times out: wrong or blocked port. Use 587 with STARTTLS.
- Sending stops mid-campaign: you’ve hit a rate or daily limit. Slow down and spread the volume.
Where SMTP stops being enough
These settings send fine from one Outlook mailbox through an app. But cold outreach at volume is a different job, and running it through a single SMTP connection concentrates all your sending on one inbox, which damages its reputation fast. The 10,000-a-day ceiling also caps you before real scale.
Serious outbound spreads a sensible daily volume across several warmed-up inboxes. HotHawk connects your Microsoft inboxes over OAuth (so the 2026 auth change is a non-issue), warms them up on real inboxes, and uses inbox rotation to spread sending across all of them, keeping each one healthy while your total reach climbs. A cold email sequencer runs the campaign and every reply arrives in one Master Inbox.
Connect your Microsoft inboxes and send, OAuth ready
HotHawk connects Microsoft inboxes over OAuth, warms them up, and rotates your sending, so the 2026 auth change never touches you. Start free, no card needed.
Start your 7 day free trialA few common questions
What is the SMTP server for Outlook?
Microsoft 365 business accounts use smtp.office365.com; personal Outlook.com uses smtp-mail.outlook.com. Both use port 587 with STARTTLS, and your username is your full email address.
Is Microsoft turning off basic authentication for SMTP? Yes. Basic authentication (username and password) for SMTP submission is being retired through 2026, moving to disabled-by-default, with OAuth 2.0 as the replacement. Check Microsoft’s current documentation for exact dates.
Why do I get “550 5.7.30 Basic authentication is not supported”? Basic auth is disabled for your tenant. The fix is to use a sending tool that connects over OAuth 2.0 rather than a stored username and password.
How many emails can I send through Outlook SMTP per day? Microsoft 365 business allows up to 10,000 recipients a day, with 500 recipients per message and around 30 messages a minute. Personal Outlook.com is far lower, roughly 300 a day.
For the same details on Google, see the Gmail SMTP settings guide, and for a primer on how SMTP works, start with SMTP settings explained. If your goal is bulk sending, read how to send bulk email in Outlook.
