[Ken Manheimer]
More importantly, after reviewing the vacation man page, i realized that the precedence: bulk header would be redundant for mailing list traffic, since most of the kinds of things that respect it also refrain from responding to messages that do not have the recipient's address explicitly mentioned among the destination addresses, which is inherently the case for maillist traffic - so the precedence: bulk is unnecessary.
I'd say inserting a "Precedence: list" header is a good thing anyway.
Consider the case of a vacation program not knowing which addresses maps to which mail users -- such a vacation program (which is not at all uncommon) would have (very nearly) no idea whether the address in the To: header is a mailing list address or some strange alias pointing to the mail user it is trying to do it's thing for. Giving such a vacation program an additional header to base it's judgement on is IMHO a good thing.
I have no idea where, or even if, "Precedence: list" is standardized in any way, but I think that thath is what majordomo is inserting. Being compatible with majordomo when it doesn't cost us anything is also, IMHO, a good thing.
The only reason I see for _not_ adding any Precedence: header, is that Mailman-delivered messages have half a truckload of headers as it is. But that, IMHO, isn't really a strong argument -- as long as all the headers are there for some good reason, they _should_ be in there.
Just my ยค.02,
Harald