How to Fix Gmail Send Mail As SMTP Authentication Fails for Microsoft 365
Question details
Users are experiencing SMTP authentication failures when attempting to use Gmail's 'Send mail as' feature to send emails through a Microsoft 365 account via smtp.office365.com.
- Product
- Microsoft 365 and Gmail
- Device & OS
- not provided
- Scenario
- Configuring Gmail to send outgoing messages using a Microsoft 365 email alias.
- Observed behavior
- SMTP authentication through smtp.office365.com is rejected, preventing emails from being sent using the Microsoft 365 address, even if the feature worked previously.
Ensure you have administrator access to the Microsoft 365 Admin Center, as resolving this issue typically requires modifying global SMTP authentication policies or mailbox-specific settings.
Enable SMTP AUTH for the Specific Microsoft 365 Mailbox
Microsoft often disables basic SMTP authentication by default for security reasons. You must manually enable SMTP AUTH for the specific mailbox you want to connect to Gmail.
Modern authentication requirements in Microsoft 365 frequently block basic SMTP connections. To allow Gmail's 'Send mail as' feature to connect, you must explicitly permit Authenticated SMTP for the targeted user account.
Log into the Microsoft 365 Admin Center using your administrator credentials.
Navigate to 'Users' > 'Active users' in the left-hand menu, and click on the user account you are trying to connect to Gmail.
In the user flyout pane, select the 'Mail' tab, and under the 'Email apps' section, click 'Manage email apps'.
Ensure the 'Authenticated SMTP' checkbox is selected. Click 'Save changes' and wait up to 30 minutes for the policy to propagate.
Reconfigure Gmail's 'Send Mail As' Settings
Remove and re-add the Microsoft 365 account in Gmail using the exact recommended SMTP server, port, and TLS encryption method.
Experience a Seamless and Free Office Alternative with WPS Office
If you are managing Microsoft 365 settings and find the subscription costs or administrative complexities frustrating, WPS Office offers a powerful, lightweight, and completely free alternative for your daily productivity needs.
- 1. Download WPS Office: Visit the official WPS website and download the free installer for your operating system.
- 2. Install the Software: Run the setup file and follow the on-screen prompts to complete the installation in seconds.
- 3. Open Your Documents: Launch WPS Office and instantly open your existing Microsoft Office files with perfect formatting preservation.
Frequently Asked Questions
Why does smtp.office365.com keep rejecting my Gmail connection?
Microsoft 365 has likely disabled basic authentication (SMTP AUTH) for your tenant as a default security measure. You need to explicitly enable Authenticated SMTP in the Microsoft 365 Admin Center for the specific user mailbox to allow Gmail to connect.
Can I use 'Send mail as' in Gmail if I have Multi-Factor Authentication (MFA) enabled?
Yes, but you cannot use your regular Microsoft 365 login password. You must generate a dedicated App Password in your Microsoft 365 security settings and paste that into Gmail's SMTP configuration window.
What are the correct SMTP settings for Microsoft 365 in Gmail?
You must use 'smtp.office365.com' as the SMTP server, select port 587, and choose the 'Secured connection using TLS' option. Using port 25 or SSL may result in connection failures.
What should I do if my Microsoft 365 subscription is managed by a reseller like GoDaddy?
If a reseller manages your tenant, you may not have direct access to enable SMTP AUTH. You will need to log into the reseller's specific dashboard to adjust email security settings or contact their support team to enable Authenticated SMTP on your behalf.
