check before: 2026-03-01
Product:
Exchange, Microsoft 365 admin center
Platform:
Developer, Online, World tenant
Status:
Change type:
Admin impact, Retirement, Updated message, User impact
Links:
Details:
Summary:
Exchange Online will retire Basic Auth for Client Submission (SMTP AUTH) starting March 1, 2026, with full rejection by April 30, 2026. Customers must switch to OAuth or other alternatives. The SMTP AUTH Clients Submission Report now includes an Authentication Protocol column to assist in this transition.
Details:
Updated June 12, 2025: We have delayed the Basic Auth removal from SMTP AUTH Client Submission to begin March 1st 2026 and complete by April 30th 2026 in order to give customers more time to adopt alternatives. Expect no further delays beyond this date. Please review the information below for more details.
Updated October 18, 2024: We have updated the SMTP AUTH Clients Submission Report in the Exchange admin center, adding the Authentication Protocol column to show if Basic auth or OAuth is being used to submit email to Exchange Online. The data will build up over the next 90 days. Thank you for your patience.
Today, we are announcing that Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) gradually beginning with a small percentage of submission rejections for all tenants on March 1st 2026 and reaching 100% rejections on April 30th 2026, (previously September 2025). After this time, applications and devices will no longer be able to use Basic auth as an authentication method and must use OAuth when using SMTP AUTH to send email.
Basic auth is a legacy authentication method that sends usernames and passwords in plain text over the network. This makes it vulnerable to credential theft, phishing, and brute force attacks. To improve the protection of our customers and their data, we are retiring Basic auth from Client Submission (SMTP AUTH) and encouraging customers to use modern authentication methods that are more secure.
[When this will happen:]
We will be making this change beginning March 1st, 2026, and completing April 30th, 2026 (previously September 2025).
Change Category:
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Scope:
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Release Phase:
Created:
2024-04-26
updated:
2025-06-13
Task Type
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Docu to Check
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MS How does it affect me
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MS Preperations
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MS Urgency
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MS workload name
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More Info URL
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summary for non-techies**
Microsoft is phasing out Basic Authentication for Exchange Online in favor of OAuth, starting March 1, 2026, to enhance email security by using tokens instead of plain text passwords, with full rejection of Basic Authentication by April 30, 2026.
Direct effects for Operations**
Retirement of Basic Auth for SMTP AUTH
Users relying on Basic Auth for email submission will face disruptions in sending emails, leading to potential communication breakdowns.
- roles: Email Administrators, End Users
- references: https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online
Increased Security Risks
Without proper transition to OAuth, users may experience increased vulnerability to phishing and credential theft, impacting overall security posture.
- roles: Security Administrators, End Users
- references: https://learn.microsoft.com/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth
Email Delivery Failures
Clients using Basic Auth will receive rejection responses, causing delays in email delivery and potential loss of important communications.
- roles: Email Administrators, Support Staff
- references: https://learn.microsoft.com/exchange/mail-flow-best-practices/high-volume-mails-m365
User Experience Degradation
Users may experience frustration and confusion due to sudden inability to send emails, leading to decreased productivity.
- roles: End Users, IT Support Staff
- references: https://learn.microsoft.com/azure/communication-services/concepts/email/email-overview
Need for Immediate Training and Support
Organizations will need to provide immediate training on OAuth alternatives, straining IT resources and impacting user experience.
- roles: Training Coordinators, IT Support Staff
- references: https://learn.microsoft.com/exchange/mail-flow/connectors/allow-anonymous-relay?view=exchserver-2019
Configutation Options**
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Potentional Risks**
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IT Security**
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explanation for non-techies**
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** AI generated content. This information must be reviewed before use.
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change history
| Date | Property | old | new |
| 2025-06-13 | MC Messages | Updated October 18, 2024: We have updated the SMTP AUTH Clients Submission Report in the Exchange admin center, adding the Authentication Protocol column to show if Basic auth or OAuth is being used to submit email to Exchange Online. The data will build up over the next 90 days. Thank you for your patience.
Today, we are announcing that Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) in September 2025. After this time, applications and devices will no longer be able to use Basic auth as an authentication method and must use OAuth when using SMTP AUTH to send email. Basic auth is a legacy authentication method that sends usernames and passwords in plain text over the network. This makes it vulnerable to credential theft, phishing, and brute force attacks. To improve the protection of our customers and their data, we are retiring Basic auth from Client Submission (SMTP AUTH) and encouraging customers to use modern authentication methods that are more secure. [When this will happen:] We will be making this change in September 2025. | Updated June 12, 2025: We have delayed the Basic Auth removal from SMTP AUTH Client Submission to begin March 1st 2026 and complete by April 30th 2026 in order to give customers more time to adopt alternatives. Expect no further delays beyond this date. Please review the information below for more details.
Updated October 18, 2024: We have updated the SMTP AUTH Clients Submission Report in the Exchange admin center, adding the Authentication Protocol column to show if Basic auth or OAuth is being used to submit email to Exchange Online. The data will build up over the next 90 days. Thank you for your patience. Today, we are announcing that Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) gradually beginning with a small percentage of submission rejections for all tenants on March 1st 2026 and reaching 100% rejections on April 30th 2026, (previously September 2025). After this time, applications and devices will no longer be able to use Basic auth as an authentication method and must use OAuth when using SMTP AUTH to send email. Basic auth is a legacy authentication method that sends usernames and passwords in plain text over the network. This makes it vulnerable to credential theft, phishing, and brute force attacks. To improve the protection of our customers and their data, we are retiring Basic auth from Client Submission (SMTP AUTH) and encouraging customers to use modern authentication methods that are more secure. [When this will happen:] We will be making this change beginning March 1st, 2026, and completing April 30th, 2026 (previously September 2025). |
| 2025-06-13 | MC How Affect | In September 2024, we will update the SMTP AUTH Clients Submission Report in the Exchange admin center to show if Basic auth or OAuth is being used to submit email to Exchange Online. In January 2025, we will send a Message Center post to tenants who are using Basic auth with Client Submission (SMTP AUTH) to alert them to the upcoming change. In August 2025, about 30 days before we disable Basic auth we will send another Message Center post to tenants who are still using Basic auth with Client Submission (SMTP AUTH).
During September 2025, we will remove support for Basic auth with the Client Submission (SMTP AUTH) endpoints: smtp.office365.com smtp-legacy.office365.com Once Basic auth is permanently disabled, any clients or apps connecting using Basic auth with Client Submission (SMTP AUTH) will receive this response: 550 5.7.30 Basic authentication is not supported for Client Submission. | The SMTP AUTH Clients Submission Report in the Exchange admin center has been updated to show if Basic auth or OAuth is being used to submit email to Exchange Online. Starting in July 2025, we will send monthly Message Center posts to tenants who are using Basic auth with Client Submission (SMTP AUTH) to alert them to the upcoming change.
Starting March 1st 2026 (previously September 2025) we will gradually start rejecting Basic Auth requests to the Client Submission (SMTP AUTH) endpoints, increasing to 100% rejection by the end of the April 2026. The Client Submission (SMTP AUTH) endpoints in scope for this change are: * smtp.office365.com * smtp-legacy.office365.com Once Basic auth is permanently disabled, any clients or apps connecting using Basic auth with Client Submission (SMTP AUTH) will receive this response: * 550 5.7.30 Basic authentication is not supported for Client Submission. |
| 2025-06-13 | MC Last Updated | 10/18/2024 18:26:45 | 2025-06-12T19:33:31Z |
| 2025-06-13 | MC prepare | If your client supports OAuth, follow these steps: Authenticate an IMAP, POP or SMTP connection using OAuth
If your client doesn't support OAuth and you must use Basic Auth with Client Submission (SMTP AUTH), you will need to switch to one of the following alternatives before September 2025: If you are using basic authentication with Client Submission (SMTP AUTH) to send emails to recipients internal to your tenant, you can use Microsoft 365 High Volume Email. Please visit this site to learn more: Manage high volume emails for Microsoft 365 Public preview If you are using basic authentication with Client Submission (SMTP AUTH) to send emails to recipients internal and external to your tenant, you can use Azure Communication Services Email. Please visit this site to learn more: Overview of Azure Communication Services email If you have an Exchange Server on-premises in a hybrid configuration, you can use Basic auth to authenticate with the Exchange Server on-premises or configure the Exchange Server on-premises with a Receive connector that allows anonymous relay on Exchange servers. Please visit this site to learn more: Allow anonymous relay on Exchange servers Regardless of the volume of email, if you must use Basic auth to send email with Exchange Online, then you must use one of the alternatives. We understand that this change requires some adjustments, but we believe that this is a necessary step to enhance the security and reliability of our email service and your data. https://learn.microsoft.com/azure/communication-services/concepts/email/email-overview https://learn.microsoft.com/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth https://learn.microsoft.com/exchange/mail-flow/connectors/allow-anonymous-relay?view=exchserver-2019 https://learn.microsoft.com/Exchange/mail-flow-best-practices/high-volume-mails-m365 | If your client supports OAuth, follow these steps: Authenticate an IMAP, POP or SMTP connection using OAuth
If your client doesn't support OAuth and you must use Basic Auth with Client Submission (SMTP AUTH), you will need to switch to one of the following alternatives before April 2026, previously September 2025: * If you are using basic authentication with Client Submission (SMTP AUTH) to send emails to recipients internal to your tenant, you can use Microsoft 365 High Volume Email. Please visit this site to learn more: Manage high volume emails for Microsoft 365 Public preview * If you are using basic authentication with Client Submission (SMTP AUTH) to send emails to recipients internal and external to your tenant, you can use Azure Communication Services Email. Please visit this site to learn more: Overview of Azure Communication Services email * If you have an Exchange Server on-premises in a hybrid configuration, you can use Basic auth to authenticate with the Exchange Server on-premises or configure the Exchange Server on-premises with a Receive connector that allows anonymous relay on Exchange servers. Please visit this site to learn more: Allow anonymous relay on Exchange servers Regardless of the volume of email, if you must use Basic auth to send email with Exchange Online, then you must use one of the alternatives or a 3P solution. We understand that this change requires some adjustments, but we believe that this is a necessary step to enhance the security and reliability of our email service and your data. https://learn.microsoft.com/azure/communication-services/concepts/email/email-overview https://learn.microsoft.com/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth https://learn.microsoft.com/exchange/mail-flow/connectors/allow-anonymous-relay?view=exchserver-2019 https://learn.microsoft.com/Exchange/mail-flow-best-practices/high-volume-mails-m365 |
| 2025-06-13 | MC Summary | Exchange Online will retire Basic Auth for SMTP AUTH in September 2025. Users must switch to OAuth or other alternatives. The SMTP AUTH Clients Submission Report in the Exchange admin center will indicate the authentication method used. This change aims to enhance security against vulnerabilities associated with Basic Auth. | Exchange Online will retire Basic Auth for Client Submission (SMTP AUTH) starting March 1, 2026, with full rejection by April 30, 2026. Customers must switch to OAuth or other alternatives. The SMTP AUTH Clients Submission Report now includes an Authentication Protocol column to assist in this transition. |
| 2024-10-19 | MC Messages | Today, we are announcing that Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) in September 2025. After this time, applications and devices will no longer be able to use Basic auth as an authentication method and must use OAuth when using SMTP AUTH to send email.
Basic auth is a legacy authentication method that sends usernames and passwords in plain text over the network. This makes it vulnerable to credential theft, phishing, and brute force attacks. To improve the protection of our customers and their data, we are retiring Basic auth from Client Submission (SMTP AUTH) and encouraging customers to use modern authentication methods that are more secure. [When this will happen:] We will be making this change in September 2025. | Updated October 18, 2024: We have updated the SMTP AUTH Clients Submission Report in the Exchange admin center, adding the Authentication Protocol column to show if Basic auth or OAuth is being used to submit email to Exchange Online. The data will build up over the next 90 days. Thank you for your patience.
Today, we are announcing that Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) in September 2025. After this time, applications and devices will no longer be able to use Basic auth as an authentication method and must use OAuth when using SMTP AUTH to send email. Basic auth is a legacy authentication method that sends usernames and passwords in plain text over the network. This makes it vulnerable to credential theft, phishing, and brute force attacks. To improve the protection of our customers and their data, we are retiring Basic auth from Client Submission (SMTP AUTH) and encouraging customers to use modern authentication methods that are more secure. [When this will happen:] We will be making this change in September 2025. |
| 2024-10-19 | MC Title | Exchange Online to retire Basic Auth for Client Submission (SMTP AUTH) | (Updated) Exchange Online to retire Basic Auth for Client Submission (SMTP AUTH) |
| 2024-10-19 | MC Last Updated | 04/26/2024 02:17:12 | 2024-10-18T18:26:45Z |
| 2024-10-19 | MC MessageTagNames | User impact, Admin impact, Retirement | Updated message, User impact, Admin impact, Retirement |
| 2024-10-19 | MC Summary | Exchange Online will retire Basic Auth for Client Submission (SMTP AUTH) in September 2025. Users must switch to OAuth or other alternatives before this date, as applications using Basic Auth will no longer be supported. Steps to prepare and alternative options are provided. | Exchange Online will retire Basic Auth for SMTP AUTH in September 2025. Users must switch to OAuth or other alternatives. The SMTP AUTH Clients Submission Report in the Exchange admin center will indicate the authentication method used. This change aims to enhance security against vulnerabilities associated with Basic Auth. |
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