Outlook SMTP settings let you send email through Microsoft’s servers using any email client, website, or application that supports the Simple Mail Transfer Protocol. The core configuration requires server address smtp-mail.outlook.com, port 587, STARTTLS encryption, and your full Outlook email address as the username.
SMTP handles outgoing email exclusively — the “sending” half of your email infrastructure. Whether you’re configuring a WordPress contact form, connecting Thunderbird to your Outlook account, or setting up a CRM to send through Microsoft’s servers, correct settings determine whether messages transmit successfully or fail silently.
The configuration works for personal Outlook.com accounts and Microsoft 365 business subscriptions, though the server addresses differ slightly between them.
Getting settings right matters because incorrect configuration means emails fail without warning — contact forms stop working, CRM notifications never send, and you won’t know until someone complains.
Standard Outlook.com SMTP configuration requires:
- Port: 587
- Encryption: STARTTLS
- Authentication: Required
- Server: smtp-mail.outlook.com
- Username: Full Outlook email address
- Password: Microsoft password (or app password with 2FA)
What are the correct Outlook SMTP server settings?
The correct Outlook SMTP settings depend on whether you’re using a free Outlook.com account or a Microsoft 365 business subscription. Both configurations require authentication and encryption, but server addresses differ between consumer and business accounts.
| Setting | Outlook.com (free) | Microsoft 365 (business) |
| SMTP server | smtp-mail.outlook.com | smtp.office365.com |
| Port | 587 | 587 |
| Encryption | STARTTLS | STARTTLS |
| Authentication | Required | Required |
| Username | Full email address | Full email address |
Server addresses
Microsoft maintains separate server addresses for consumer and business accounts. The smtp-mail.outlook.com server handles personal accounts (@outlook.com, @hotmail.com, @live.com), while smtp.office365.com serves Microsoft 365 subscribers with custom domains.
Using the wrong server address causes authentication failures even when credentials are correct. If connection attempts fail repeatedly, verify you’re using the server matching your account type — a common oversight when copying settings from generic tutorials.
Port selection
Port 587 represents the modern standard for email submission, and the only port Microsoft officially supports for Outlook SMTP. The port requires authentication before accepting messages (preventing unauthorized relay) and supports STARTTLS encryption that secures data during transmission.
Older documentation sometimes references port 25 or port 465, but Microsoft recommends against both. Port 25 is blocked by most ISPs for residential users as a spam prevention measure. Port 465 uses a deprecated encryption method that causes compatibility issues with modern clients.
Why does port 587 matter for Outlook SMTP?
Port 587 matters because it represents the modern standard for authenticated email submission — and Microsoft requires it for all Outlook SMTP connections. The port enforces authentication before accepting messages, which prevents servers from becoming open relays that spammers could exploit.
| Port | Purpose | Security | Outlook support |
| 587 | Client submission | STARTTLS (upgrades to TLS) | Recommended |
| 25 | Server-to-server relay | Often unencrypted | Blocked by most ISPs |
| 465 | Legacy SMTPS | Implicit TLS | Not recommended |
| 2525 | Fallback alternative | STARTTLS | Unofficial backup |
STARTTLS encryption
Port 587 uses STARTTLS, which starts as a plain-text connection and “upgrades” to encrypted communication after the initial handshake. The encryption protects credentials and message content from interception during transmission — important when sending through shared networks or public Wi-Fi.
The alternative (port 465’s implicit TLS) encrypts from the very first byte, which sounds better but creates compatibility problems with some email clients. Microsoft chose STARTTLS as the standard because it works reliably across different software configurations.
ISP blocking
Most Internet Service Providers block port 25 for residential and small business connections.
The blocking prevents compromised computers on home networks from sending spam, but it also means port 25 won’t work for legitimate email sending from those connections (even if your settings are technically correct).
If port 587 is blocked by your network — rare, but some corporate firewalls restrict it — port 2525 serves as an unofficial fallback. The port isn’t standardized, but many email providers accept connections there with the same STARTTLS encryption that port 587 uses.
How do you configure Outlook SMTP in desktop clients?
Configuring Outlook SMTP in desktop email clients requires navigating to account settings and manually entering server information. The process varies slightly between applications, but all require the same core settings: server address, port number, encryption method, and authentication credentials.
Thunderbird setup
Mozilla Thunderbird auto-detects many configurations, but Outlook.com often requires manual input for reliable SMTP. Navigate to Account Settings by right-clicking your account in the folder pane, then select Outgoing Server (SMTP) at the bottom of the list.
Click Add to create a new SMTP server entry:
- Port: 587
- Connection security: STARTTLS
- Server Name: smtp-mail.outlook.com
- User Name: Full Outlook email address
- Authentication method: Normal password
After saving, return to your account settings and select the new SMTP server from the “Outgoing Server” dropdown. Send a test email to verify the configuration works before assuming everything is set.
Outlook desktop
The Outlook desktop application usually configures itself automatically when you add a Microsoft account, but manual SMTP settings become necessary when connecting through third-party integrations or troubleshooting connection issues.
Open File → Account Settings → Account Settings, select your email account, and click Change. Then click More Settings and navigate to the Outgoing Server tab.
Check “My outgoing server (SMTP) requires authentication” and verify “Use same settings as my incoming mail server” is selected. Under the Advanced tab, confirm the outgoing server port shows 587, and the encryption type shows STARTTLS.
Apple Mail
macOS Mail requires manual SMTP configuration when automatic setup fails (common with Outlook.com accounts). Go to Mail → Settings → Accounts, select your Outlook account, then click Server Settings.
Under Outgoing Mail Server (SMTP), uncheck “Automatically manage connection settings” and enter:
- Host Name: smtp-mail.outlook.com
- Port: 587
- Use TLS/SSL: Checked
- Authentication: Password
How do you configure Outlook SMTP for WordPress?
WordPress sites need SMTP configuration to send emails reliably because the default PHP mail function fails frequently — it lacks authentication and often triggers spam filters on the receiving end. Configuring Outlook SMTP for WordPress requires a plugin and your Microsoft account credentials.
The WP Mail SMTP plugin (most popular option) handles configuration through a visual interface. After installation, navigate to WP Mail SMTP → Settings and select “Other SMTP” as your mailer.
Plugin settings
Enter your Outlook SMTP credentials in the plugin configuration panel using the values below.
| Field | Value |
| SMTP Host | smtp-mail.outlook.com |
| Encryption | TLS |
| SMTP Port | 587 |
| Auto TLS | On |
| Authentication | On |
| SMTP Username | Full Outlook email address |
| SMTP Password | Microsoft password (or app password) |
The “From Email” field should match your Outlook address exactly — mismatched addresses often cause authentication failures or trigger spam filters on the receiving end.
Testing connection
After saving settings, use the plugin’s Email Test feature to send a test message. Successful delivery confirms your configuration works. Failed tests typically indicate one of three issues:
- Firewall blocking port 587
- Hosting provider restricting outbound SMTP connections
- Incorrect password (especially without an app password when 2FA is enabled)
Some shared hosting environments block outbound SMTP entirely as a spam prevention measure. If your host blocks port 587, you may need to use their built-in SMTP relay, upgrade to a host that allows outbound email, or switch to a dedicated transactional email service.
What authentication does Outlook SMTP require?
Outlook SMTP requires authentication for every connection — you cannot send email anonymously through Microsoft’s servers. The authentication method depends on your account security configuration, particularly whether you’ve enabled two-factor authentication (2FA).
Standard authentication
Accounts without two-factor authentication can use regular Microsoft passwords directly in SMTP settings. Enter your full email address as the username and your account password — the same credentials you use to log into outlook.com in a browser.
However, Microsoft strongly encourages 2FA for all accounts. If you enable it later, existing SMTP configurations stop working until you generate app passwords (a detail that catches many users off guard when security settings change).
App passwords
Two-factor authentication creates a complication — SMTP clients can’t complete the second verification step because they don’t know how to receive SMS codes or authenticator prompts. App passwords solve the problem by generating a special 16-character password that bypasses 2FA for specific applications.
To generate an app password:
- Sign in to your Microsoft account at account.microsoft.com
- Navigate to Security → Advanced security options
- Under App passwords, click “Create a new app password”
- Copy the generated password immediately (it won’t appear again)
Use the app password in your SMTP configuration instead of your regular account password. Each application should have its own app password — if you need to revoke access later, you can delete that specific password without affecting other integrations.
OAuth2 authentication
Modern email clients increasingly support OAuth2, which handles authentication through a browser-based login flow rather than stored passwords.
OAuth2 is more secure (your password never gets stored in the email client) and works naturally with 2FA without requiring app passwords.
Not all applications support OAuth2 yet, particularly older software and many WordPress plugins. When OAuth2 is available, prefer it over password-based authentication for better security and fewer maintenance headaches when passwords change.
What are the sending limits for Outlook SMTP?
Microsoft imposes sending limits that affect how you can use Outlook SMTP for high-volume applications. The limits exist to prevent spam abuse and maintain server performance, but they also constrain legitimate bulk sending in ways that matter for enterprise operations.
| Account type | Daily limit | Recipients per message | Attachment size |
| Outlook.com (free) | 300 emails | 100 recipients | 25 MB |
| Microsoft 365 Business | 10,000 emails | 500 recipients | 25 MB |
Free account limits
Free Outlook.com accounts face strict quotas: 300 emails per day maximum, with no more than 100 recipients on any single message. The limits make Outlook.com unsuitable for bulk email campaigns, newsletters, or high-volume transactional sending.
Exceeding the limit triggers temporary blocks lasting 24 hours or longer. Repeated violations can result in permanent account suspension — Microsoft monitors for patterns suggesting spam or abuse, and automated systems respond without warning.
Business account limits
Microsoft 365 business subscriptions allow significantly higher volume (up to 10,000 messages daily), but the quotas still fall short for true high-volume operations. Organizations sending tens of thousands of emails need dedicated email infrastructure beyond Microsoft’s standard offering.
The limits reset daily, though there’s no exact time specified — planning around the reset requires monitoring actual sending patterns.
Organizations running sophisticated email programs through platforms like Salesforce Marketing Cloud or Marketo typically use Outlook SMTP for auxiliary functions (internal notifications, CRM alerts) rather than primary campaign sending.
Bulk alternatives
If sending requirements exceed Outlook’s limits, dedicated infrastructure becomes necessary. Transactional email services (SendGrid, Amazon SES, Mailgun) handle high volume without the restrictions that consumer and small-business email platforms impose.
The tradeoff involves cost and complexity, but organizations sending 50K+ emails monthly usually find dedicated services more reliable than pushing against Outlook’s quotas. The cost of a dedicated service often runs less than the revenue lost when emails don’t arrive.
Why do Outlook SMTP emails sometimes fail?
Outlook SMTP failures typically trace to authentication problems, port blocking, or configuration mismatches. Understanding common failure modes helps diagnose issues faster when email suddenly stops sending — and prevents the panicked troubleshooting that wastes hours on the wrong problem.
Authentication errors
The most frequent cause of SMTP failure involves credentials. Authentication errors occur when:
- Your password changed and wasn’t updated in SMTP settings
- You enabled 2FA without generating an app password
- Your username doesn’t include the full email address
- The app password expired or was revoked
Microsoft’s error messages during authentication failure are often vague (“Authentication unsuccessful” covers many possibilities), so systematic checking of credentials usually proves the fastest diagnostic approach.
Port blocking
Some networks block outbound connections on port 587 as a security measure. Corporate firewalls, university networks, and certain hosting providers restrict SMTP ports to prevent malware from sending spam through compromised machines.
Testing from a different network (mobile hotspot, home connection) quickly identifies whether port blocking causes your issue. If port 587 is blocked, port 2525 sometimes works as an alternative — though some restrictive networks block all SMTP ports entirely.
Sender reputation
Even when configuration is correct, emails can fail delivery at the recipient end if your sending reputation is poor. Microsoft’s servers accept your message, but Gmail or another provider rejects it based on SPF record misconfiguration, missing DKIM authentication, or negative reputation history.
Reputation problems manifest as “delivered but spam-foldered” rather than outright failures — the SMTP transaction succeeds, but recipients never see your message. Testing with an email deliverability test reveals where messages actually land across different providers.
Configuration is only half the deliverability equation
Outlook SMTP settings determine whether emails leave your application successfully. Deliverability — whether those emails reach recipient inboxes — depends on sender reputation, authentication, and sending patterns that extend beyond basic configuration.
Organizations sending significant volume through Outlook (or any SMTP server) often discover that correct settings don’t guarantee inbox placement.
New sending domains need reputation building through gradual email warmup. Authentication records need proper configuration at the DNS level. Sending patterns need ramping rather than sudden bursts that trigger spam filters.
EmailWarmup.com helps senders build the reputation that determines deliverability:
- Inbox rates up to 98% on Pro accounts
- Free deliverability test across 50+ providers
- 24/7 human support from deliverability specialists
- Personalized email warmup matching your sending patterns
Correct SMTP settings get your emails out the door. Reputation determines whether anyone sees them.
Schedule a free consultation with an email deliverability consultant today.
Frequently asked questions
Here are some commonly asked questions about Outlook SMTP:
The SMTP server address for free Outlook.com accounts is smtp-mail.outlook.com. Microsoft 365 business accounts use smtp.office365.com instead. Both require port 587 with STARTTLS encryption and full authentication using your email address and password (or app password if two-factor authentication is enabled).
If you’ve enabled two-factor authentication on your Microsoft account, your regular password won’t work for SMTP connections because the client can’t complete the second verification step. Generate an app password from your Microsoft account security settings at account.microsoft.com and use that 16-character code instead of your normal password.
Not effectively. Free Outlook.com accounts limit sending to 300 emails daily with 100 maximum recipients per message. Microsoft 365 business accounts allow up to 10,000 daily, but that still falls short for serious bulk sending. High-volume campaigns require dedicated transactional email services designed for scale.
Port 587 with STARTTLS encryption is the only officially supported option for Outlook SMTP. Port 25 is blocked by most ISPs for residential users, and port 465 uses a deprecated encryption method. If your network blocks port 587, port 2525 sometimes works as an unofficial fallback with identical encryption.
Send a test email through whatever application you’ve configured. Most email clients have a “Send Test Email” function in SMTP settings. For WordPress, plugins like WP Mail SMTP include built-in testing. If tests fail, verify your server address matches your account type, confirm port 587 with STARTTLS, and check whether you need an app password for 2FA-enabled accounts.
