I have occasional outside contact, once a month on average, and it has not changed our relationship at all. I feel reassured that I can depend on her if I need contact between sessions. I've been seeing her for almost three years and the boundaries haven't changed.

I don't think you can extrapolate from what happens on these forums. If you're able to have outside contact and not obsess about how quickly your T responds, or overanalyze every word of their email, then it can be a useful support. If you think you'd be prone to obsessing, I think it called for a conversation with your T.

It probably calls for a conversation with T regardless.