Outlook SMTP & IMAP Settings at a Glance
| Setting | Outlook.com (personal) | Microsoft 365 (work) |
|---|---|---|
| SMTP server | smtp-mail.outlook.com | smtp.office365.com |
| SMTP port | 587 (STARTTLS) | |
| IMAP server | imap-mail.outlook.com | outlook.office365.com |
| IMAP port | 993 (SSL/TLS) | |
| POP3 server / port | pop-mail.outlook.com | outlook.office365.com · 995 (SSL) |
| Username / password | Full email address + app password (if MFA is on) | |
Confirm a working connection with our free SMTP tester and IMAP tester.
Create an App Password (Required with MFA)
If multi-factor authentication is enabled — standard on most Microsoft 365 tenants — SMTP/IMAP clients can't use your normal password. Generate an app password:
- Go to account.microsoft.com/security (personal) or your My Account → Security info (work).
- Select App passwords → Create a new app password.
- Copy the generated password and use it in place of your normal password.
Note: Microsoft 365 admins must also ensure Authenticated SMTP is enabled per-mailbox (Admin center → Active users → Mail → Manage email apps).
Common Outlook SMTP Errors and Fixes
- "535 5.7.139 Authentication unsuccessful": Authenticated SMTP is disabled for the mailbox, or you're not using an app password. Enable SMTP AUTH and use an app password.
- "550 5.7.708 Service unavailable": the sending IP is throttled or blocklisted. Warm the account and reduce volume.
- Connection refused on port 587: firewall blocking outbound SMTP — allow 587, or try the secure submission path your client supports.
- Sends work but replies don't sync: IMAP isn't configured. Add the IMAP server above and verify with an IMAP test.
Using Outlook for Cold Email
Microsoft 365 enforces a 10,000-recipient daily limit and 30 messages/minute per mailbox — but as with Gmail, the safe cold-email volume is far lower and depends on reputation. Connect your Outlook mailbox to DitLead with the SMTP/IMAP settings above, keep it on the warmup network, and rotate across multiple mailboxes to scale.
FAQs
What is the Outlook SMTP server and port?
smtp-mail.outlook.com (personal) or smtp.office365.com (work), port 587 with STARTTLS.
Does Outlook SMTP need an app password?
Yes, whenever multi-factor authentication is enabled on the account.
What is the Microsoft 365 sending limit?
10,000 recipients per day and 30 messages per minute per mailbox — far above the safe cold-email volume.