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Your message wasn't delivered because the recipient's email provider rejected it
Dear all, Recently, I registered 1 account Office 365 trial to experience O365 E3 version before bought it, I create a sharepoint site, upload some document and share with somebody, both the same...
alecsu2017 I believe MS has made some changes and you can no longer send emails from an .onmicrosoft.com email address.
Add and verify a domain and you should be able to send emails with that email address.
Deepak
I too had the same issue and i had to use a custom domain to be able to send emails.