Office 365 you weren’t recognized as a valid sender

Had a user who started to get this message. “Your message couldn’t be delivered because you weren’t recognized as a valid sender”. Logged into their Office 365 Admin account and went to Protection >> Action Center. Saw the user there and clicked “unblock” them. It took a minute, and came back with the user still in the list. I tried to send an email at the user and got the same error. In the Admin panel >> Action Center the user was still listed. I clicked “unblockagain and this time the user wasn’t listed. I tried to send another email, and got the same error again. I see a alert on the Action Center page to go to the new “Restricted Users page“. This page didn’t show the user being blocked.

I looked at the error in the Non-Deliverable Report in the returned email. The error in the message is “550 5.1.8 Access denied, bad outbound sender“.

This page was a help to let me know it could take a few hours for the email to resume.

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Phishing Attempts From

We had a customer complaining about emails stuck in the spam filter. They were getting an email with the subject line “(3) Incoming messages failed to sync”. In the email was a button to “Restore Messages”; however, when we hovered over the link the web address was for “…”.

We told the customer this was a Phishing attempt, and to not click on that button. They are ready had. We ran a full Vipre scan on their machine.

The URL takes you to a site that Google has already flagged.

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