... in order to avoid declaratory judgment jurisdiction, I recommend sticking to exactly what the court stated doesn't constitute grounds for a declaratory judgment action: "a communication from a patent owner to another party, merely identifying its patent and the other party's product line".
This advice follows a Federal Circuit case that erupted last year after Texas-based patent-holder Acceleron wrote a letter to an alleged infringer, Hewlett-Packard, which only (i) brought the pertinent patent to the attention of HP, (ii) requested a dialogue and (iii) requested a confirmation that no "case or controversy" existed at the moment. Following further correspondence HP filed a declaratory action in Delaware. This did not please Acceleron, which claimed there was no "case or controversy" since it didn't actually threaten to sue or even claim that HP was infringing.
The Federal Circuit disagreed with this interpretation of the facts, for the following reasons: (1) Acceleron stated the patent was relevant to HP's product(s) [this is presumably a pretty well ever-present factor in cases in which a patent owner considers that the recipient of the letter is infringing his patent]; (2) Acceleron imposed a short deadline for responding to their letter [this is likely to be interpreted as a litigation-led imposition]; (3) Acceleron insisted that HP not file suit [ditto] and (4) Acceleron was a non-competitor patent holding company [it's not clear to me what weight should be given to this factor. Surely if the parties had been market competitors, the same implication could be drawn that litigation was being contemplated?].