What are the Office 365 SMTP settings?

Server smtp.office365.com, port 587 (25 also works), STARTTLS with TLS 1.2 or 1.3, and the full email address and password (or OAuth) of a licensed mailbox. Authenticated SMTP must be enabled for that mailbox.

What is the Outlook SMTP server?

For work and school mailboxes on Microsoft 365 it is smtp.office365.com on port 587. For personal Outlook.com and Hotmail accounts it is smtp-mail.outlook.com on port 587 with STARTTLS, and Outlook.com requires Modern Auth (OAuth2).

Can I use port 465 with Office 365?

No. Microsoft says that if a device or app recommends or defaults to port 465, it does not support the TLS versions SMTP client submission requires. Use 587 with STARTTLS.

Is Microsoft turning off SMTP AUTH?

Microsoft is retiring Basic authentication (username and password) for SMTP AUTH, not SMTP AUTH itself. Its updated timeline keeps today's behaviour until December 2026, then turns Basic auth off by default for existing tenants, with admins able to re-enable it, and a final removal date to be announced in the second half of 2027. OAuth keeps working.

How many emails can I send from Office 365?

Each mailbox can send to 10,000 recipients a day, at most 30 messages a minute over SMTP AUTH, with up to 1,000 recipients per message. Mail from the default onmicrosoft.com domain is held to 100 external recipients a day per organisation.

Why do I get 5.7.57 or 535 5.7.3?

The server did not accept the sign-in. Most often Authenticated SMTP is off for the mailbox, security defaults block it, or the password is wrong. Enable SMTP AUTH for that mailbox and test the credentials in Outlook on the web.

My Microsoft 365 came from GoDaddy. Which settings do I use?

The Microsoft ones: smtp.office365.com on port 587 with STARTTLS. GoDaddy's own server (smtpout.secureserver.net) is only for GoDaddy Workspace Email.

Can I send cold email through one Office 365 mailbox?

Technically yes, but 10,000 recipients a day is Microsoft's ceiling, not a safe pace. Cold email keeps each inbox near 30 sends a day on separate lookalike domains, so you add inboxes instead of pushing one mailbox.

Office 365 SMTP Settings: smtp.office365.com, Port 587

Admin center

Five steps from off to sending

1Enable Authenticated SMTP for the mailboxMicrosoft 365 admin center, Users, Active users, pick the user, Mail, Manage email apps, tick Authenticated SMTP, save.
2Check security defaultsWith security defaults on, SMTP AUTH is off for the whole tenant. Prefer an app that signs in with OAuth.
3Enter the server detailssmtp.office365.com, port 587, STARTTLS (TLS 1.2 or 1.3).
4Sign in as the mailboxFull email address as the username. The From address must match it, or the mailbox needs Send As permission.
5Send a test emailIf it fails, match the error code to the table on this page.

Prefer PowerShell? One line per mailbox:

Exchange Online PowerShell

Set-CASMailbox -Identity jane@getacme.com -SmtpClientAuthenticationDisabled $false

admin.microsoft.com

Microsoft 365 admin center Users Active users

Jane Lee

jane@getacme.com

Manage email apps

Outlook on the web

Outlook desktop (MAPI)

Exchange Web Services

Mobile (Exchange ActiveSync)

IMAP

POP

Authenticated SMTPneeded for SMTP

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Office 365 SMTP Settings One Switch, Then Connected.

Every Microsoft mailbox.
Copy and paste.

Turn on Authenticated SMTP.
For the one mailbox that sends.

Five steps from off to sending

Office 365 SMTP errors.
Decoded, with the fix.

Outlook inboxes for cold email.
SMTP already on.

What is the Office 365 SMTP server?

Office 365 SMTP questions

Cold email from Outlook, without the admin work

Office 365 SMTP Settings One Switch, Then Connected.

Every Microsoft mailbox.Copy and paste.

Turn on Authenticated SMTP.For the one mailbox that sends.

Five steps from off to sending

Office 365 SMTP errors.Decoded, with the fix.

Outlook inboxes for cold email.SMTP already on.

What is the Office 365 SMTP server?

Office 365 SMTP questions

Cold email from Outlook, without the admin work

Every Microsoft mailbox.
Copy and paste.

Turn on Authenticated SMTP.
For the one mailbox that sends.

Office 365 SMTP errors.
Decoded, with the fix.

Outlook inboxes for cold email.
SMTP already on.