provider
Outlook SMTP Settings: The Complete Setup Guide
Getting SMTP settings wrong is one of the most common — and most avoidable — reasons a mail client or app can’t send through Outlook or Microsoft 365.
Outlook.com (personal accounts)
| Setting | Value |
|---|---|
| SMTP Server | smtp-mail.outlook.com |
| Port | 587 |
| Encryption | STARTTLS (TLS) |
| Authentication | Full email address + password (or app password) |
Microsoft 365 / Office 365 (work/school accounts)
| Setting | Value |
|---|---|
| SMTP Server | smtp.office365.com |
| Port | 587 |
| Encryption | STARTTLS (TLS) |
| Authentication | Modern auth (OAuth 2.0) increasingly required |
Important: Microsoft is phasing out basic authentication (plain username/password) for SMTP on 365 tenants. If a previously working setup suddenly fails with an authentication error, this is the most likely cause — you’ll need to switch to OAuth 2.0 or an app password, depending on your tenant’s configuration.
Common connection errors
- “Authentication failed” — usually 2FA requiring an app password, or basic auth disabled on the tenant.
- “Connection timed out” — check you’re using port 587 (not 25, which is commonly blocked by ISPs), and that STARTTLS is enabled, not implicit SSL on port 465.
- “Relay access denied” — the “from” address doesn’t match the authenticated account, or you’re trying to send as an alias that isn’t authorized.
Once it connects: check deliverability, not just connectivity
A working SMTP connection just means you can send — it says nothing about whether mail actually reaches the inbox. Confirm your domain’s SPF, DKIM, and DMARC are set up correctly, and if you’re sending meaningful volume or cold outreach from a new mailbox, warm it up first — Microsoft 365 throttles and flags accounts that ramp volume too fast.
Land in the inbox — automatically
MailPilot warms up your mailboxes across a network of real inboxes, so your emails stop hitting spam. Free to start, no credit card.
Start free warmupOutlook SMTP Settings — FAQ
What are the correct Outlook.com SMTP settings?
Server: smtp-mail.outlook.com, Port: 587, Encryption: STARTTLS (TLS), Authentication: your full Outlook.com email address and password (or an app password if 2FA is enabled).
What are the SMTP settings for Microsoft 365 / Office 365?
Server: smtp.office365.com, Port: 587, Encryption: STARTTLS. Microsoft 365 increasingly requires modern authentication (OAuth 2.0) rather than a plain username/password — basic auth for SMTP is being disabled account-by-account, so if password auth suddenly stops working, this is usually why.
Why am I getting a 'SMTP authentication failed' error?
The most common causes: using your regular password when 2FA/MFA is enabled (you need an app-specific password instead), basic authentication being disabled on your tenant (Microsoft 365), or an incorrect port/encryption combination. Double-check you're using port 587 with STARTTLS, not port 465 or a plain unencrypted connection.
Can I use Outlook/Microsoft 365 for cold email or bulk sending?
Technically yes for moderate volume, but Microsoft 365 has stricter sending limits than most dedicated ESPs and will throttle or flag accounts that send high volume too quickly. Any new or ramping Outlook/365 mailbox used for outreach should be warmed up gradually — see what email warmup is and when you need it.