I've been putting a meaningless serial number on my subject lines since my original question, but it is hard to tell if it has made much of a difference.
One of my clients' server/isps has been inserting a [SPAM] tag into the subject line of my emails. It still happened with just the serial number, it still happened when I added a date, but it stopped when it put a [NEWS] header in front of the subject. Exact subject line follows.
[News] Atlantic Technology Corners Subwoofer Market -- Mar. 27, 2006 -- 80343
I can't say if it was more or less successful than other mailings.
In another mailing used Excel to generate sequential serial numbers for each address using [opt1] in the subject line. I usually sort and edit my lists in Excel, so this was relatively easy to do.
Canton Home Theater Lifestyle Photos available for Editorial Use - Mar. 28- [Opt1]
This wasn't a formal press release, so I didn't use the [NEWS] tag, and I can't really tell how successful this was.
Is there an official list of recognized tags (I've looked and can't find one), or is a tag anything inside brackets?