encryption of email with MS word file fails to send in outlook

answer does not solve the problem. How is this going to get fixed?

For encrypted messages that fail only when a file is attached, the behavior depends on which encryption mechanism is used and which Outlook client is involved.

For Microsoft 365 consumer encryption (Encrypt / Do Not Forward in Outlook.com / Outlook on the web):

• All attachments are encrypted together with the message.
• With Encrypt, recipients using Outlook.com or Microsoft 365 accounts can open attachments normally; other recipients must use the Microsoft 365 Message Encryption portal and may need a temporary passcode.
• With Do Not Forward, Office attachments (Word, Excel, PowerPoint) remain encrypted even after download and can only be opened by recipients who have permission; non‑Office attachments (PDF, images) download without encryption.
• If recipients or their mail systems cannot handle the encrypted attachment flow (for example, they do not follow the portal instructions or cannot authenticate), delivery or access to the attachment can fail even though the encrypted message itself is delivered.

To improve success when sending encrypted Word attachments from Outlook.com / Outlook on the web:

1. Use Encrypt instead of Do Not Forward if recipients only need confidentiality and not forwarding restrictions.
2. Confirm that recipients open the message using Outlook.com, Microsoft 365, or follow the instructions in the encryption notification email (sign in with Microsoft/Google/Yahoo or use the temporary passcode).
3. If a recipient still cannot receive or open the attachment, send a link to the file stored on a secure share (for example, OneDrive or SharePoint) instead of attaching the file directly.

If S/MIME encryption is used instead of Microsoft 365 Message Encryption:

• A known “Encryption Problems” dialog can appear when there are mixed RSA/ECC S/MIME certificates. In that case, the warning can be a false positive and the message (with attachments) can still be sent by choosing to continue.

References:

• Send encrypted messages with a Microsoft 365 personal or family subscription
• "Conflicting or unsupported encryption" warning when sending an encrypted message
• Outlook fails to send attachments and inline images when sending a signed or encrypted email using Outlook for Mac