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Please check whether your email address is authorized/verified / blocked by your SMTP server
Office365 SMTP
Summary
When you configure Office365 to be your SMTP provider, the below condition is to be met:
The username that you have configured as part of SMTP settings in Office365, is the from_address that you have to configure in Chargebee.
If the above criteria are not met, the SMTP error will persist, and prevent emails from being sent.
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