Your message couldn't be delivered because you weren't recognized as a valid sender

Hi IB_123,

My name is RY, I'm an Independent Advisor and a Microsoft user like you.

Please take note that this is a public user-to-user forum and we do not work for Microsoft nor have access to any user accounts or information.

Sorry to hear that you are having issue with sending emails but let us work together to sort this out.

I just want to confirm if you are using work email account or personal email account?

If you are using work email account within your organization, you need to contact your IT Administrator to check if you are listed as Restricted user in Office 365.

They may refer on below article on how to do that:

https://docs.microsoft.com/en-us/microsoft-365/...

Please let me know if you have other questions or concerns.

Thank you!

Regards,

RY

Hallo Steve1da
Unzustellbar: XCXCXC
Delivery has failed to these recipients or groups:
*** Die E-Mail-Adresse wurde aus Datenschutzgründen entfernt. ***
This message couldn't be delivered because the sending email address was not recognized as a valid sender. The most common reason for this error is that the email address is, or was, suspected of sending spam. Contact the organization's email admin for help and give them this error message.
Egal wohin, kommen alle retour.
LG
Olaf

Hello Nicholas,

thank you for your request. As it was posted in English with this being the German language forum, can you tell us which language you would prefer our support to be in?

As for your question, can you tell us the full error message appearing when you try to send a mail via your Outlook email account from Thunderbird?

We look forward to your reply!

Best,

Carlos

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address

failed:

Beim senden eines Bildes vom Kalender kommt diese Antwort:

This is the mail system at host mailout09.t-online.de.

I'm sorry to have to inform you that your message could not

be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can

delete your own text from the attached returned message.

The mail system

<*** Die E-Mail-Adresse wurde aus Datenschutzgründen entfernt. ***>: host

microsoft-com.mail.protection.outlook.com[104.47.53.36] said: 550 5.4.1

Recipient address rejected: Access denied. AS(201806281)

[BL2NAM06FT003.Eop-nam06.prod.protection.outlook.com] (in reply to RCPT TO

command)