For background, I work as a three person team in a department of a company. We're all lawyers. There's a group mailbox that I don't have access to, because our manager "wants to limit who has access to X matters". My coworker started 6 months before I did and he has access.

Once I was given X matter to work on, it turns out, because they wanted to test whether someone could follow a procedure document that they were writing (I ended up redoing the document). Our manager told me to copy my coworker on all my matters but I'm not copied on his.

We created a new mailbox for Y matters (which I handle) and our manager told me to give him access to it, even though he doesn't do those matters.

My coworker would message me on Teams about a matter (I wouldn't be copied on the email thread), I'd share my thoughts but realize I'd never hear about it again and realized he wasnt copying me in.

Now, when he asks, (he legit copies the initial email request on teams, rather than even forwarding the matter to me) I tell him its best to ask our manager her thoughts rather than helping.

TL;DR

AITA for not helping my coworker with his work, when we're in the same department? It feels off to me, like they want my knowledge but want me to remain invisible.