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Hi,
We use the Office365 SMTP server to send e-mails
Most of the times this works without problems but every now and then it does not and we receive the following response:
5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM [xxx.eurprd07.prod.outlook.com]
If we then try again to send the same mail in exactly the same way (with the same credentials and settings) it works or sometimes we get the same error but then with a different FROM address. Like this:
5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM [AMxxx0007.eurprd07.prod.outlook.com]
5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM [AMxxx0028.eurprd07.prod.outlook.com]
5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM [AMyyy0063.eurprd01.prod.exchangelabs.com]
5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM [AMxxx0019.eurprd07.prod.outlook.com]
(I replaced possible sensitive information with 'xxx' or 'yyy')
So we send all these mails in exactly the same way with the same credentials, security settings, host, port, from address, etc. and most of the times it works but sometimes it does not.
Who can help us?