Dear respected Binaebi Akah Calkins,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
I’m sorry you’re having a problem but based on your description we can work together to resolve it.
For the situation you encountered, we deeply understand the inconvenience caused and apologize for it.
As per your description, generally, when we type @ sign before the name in the comments box and users can get a noticed mail. However, Microsoft Teams channel files associated with SharePoint online library, and may I know have you tried click on "Open in SharePoint" in your Team channel and select your Word document file> click on "Alert Me" and type a co-owner to see if the co-owners get email notification.


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We appreciate your understanding that sometimes the initial suggestions may not resolve the problem very soon. However, we can work together to narrow down and resolve the situation.
Appreciate your patience and understanding and thank you for your time and cooperation.
Sincerely,
Waqas Muhammad