Send As Gmail Alias Configuration

Jeff 16 Reputation points


I have previously setup a Gmail alias that allows me to "send as" my office365 email address. This is achieved in Gmail under "Settings", "Accounts and Imports" and "Send Mail As'". I have successfully set this up with multiple .edu outlook accounts, including my current one, and it worked well until 2 weeks ago. My other .edu outlook accounts continue to work. Only one does not work.

When I enter in the SMTP settings:

Sever name:
Port: 587
Encryption method: STARTTLS (Gmail only has options for TLS or SSL- I don't know if this is the source of the problem)

I receive the following error message: Authentication failed. Please check your username/password.
Server returned error: "334 VXNlcm5hbWU6 334 UGFzc3dvcmQ6 535 5.7.3 Authentication unsuccessful [] , code: 535"

However, my username and PW are correct. Some have suggested pinging to find the specific server I am using, but this hasn't worked. Others ( recommend contacting you or the administrator because Google is insisting on the use of genuine, correct certificates for servers. I have also seen that it might be related to two-factor authentication.

Please let me know if there's any additional information you might need to help resolve this.

Thank you.

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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2 answers

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  1. Vasil Michev 85,646 Reputation points MVP

    Select TLS as the method, and make sure that your O365 account is enabled for SMTP auth and basic authentication is not being blocked.

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  2. Zhengqi Lou-MSFT 8,856 Reputation points Microsoft Vendor

    Hi @Jeff ,

    Are there any different settings between other normal accounts and this one?
    As michev said, please also check SMTP auth has been enabled for this user.

    Authenticate your device or application directly with a Microsoft 365 or Office 365 mailbox, and send mail using SMTP AUTH client submission


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