The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 2 (2021-02-01T13:38:08). Exception Message: Cannot send mails to mail server. (The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM [SG2PR06CA0228.apcprd06.prod.outlook.com]).
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I had no issues when I tried using my Gsuite Email.
Best Answer
Did you use office 365 to relay emails? If so, the following link about the settings to send relay emails via office 365 is for your reference: How to set up a multifunction device or application to send email using Microsoft 365 or Office 365
Configure applications for SMTP relay:
Configure Office 365 connectors for SMTP relay: