The range between planes is infinite
Or, at least, that is the general consensus. This is based on the fact that non-demiplanes are infinite in extent and you can’t walk from one to the other so other planes are further away than that.
So, no he can’t message.
What, then, of connections between planes? The neck of a Bag of Holding? The wardrobe to Narnia? The Stargate? The doors in Lego Star Wars' Mos Eisley cantina?
Well, it's a DM's call as to whether these are actual physical connections that reduce the range to zero at that point or if they are magical connections that are infinitely far apart but allow you to cross. If the former, then sticking your hand into a Bag of Holding keeps it about 3 feet from your shoulder, if the latter then your fingers are infinitely far from your brain but they still work because magic. A DM can decide that all portals are this or all are that or take each case on its merits.