The mailing list is quite busy. (I picked a weekday at random and there were 28 emails during that day.) You can always choose to not read posts or threads that are interesting, or save mails for a rainy day.
However, if you just want to know about upcoming meetings, there is an announcement-only list you might want to join. This usually receives no more than five or six posts a month.
Subscribers to london.pm automatically receive london.pm-announce mails.
Pretty much anything, even Perl. Some people think that if a post is getting off-topic it's nice to put a notice in the subject line (eg 'POLITICS') but sometimes this isn't practical. However, you should always do this for job adverts: see below.
There are some loosely-applied rules that it's strongly suggested you follow.
Please avoid short, content-free replies. If you want to thank someone, it can be done perfectly well off list. We also have an IRC channel for banter.
Please don't use HTML in mails, and if you have to, include a text/plain equivalent. People don't like it in single mails, and they really don't like it in digests. Do you really need to use formatting?
Be considerate with quoting and trimming. You may need to trim quoted text so that people with small terminals can see that you have included a reply. Also, interleaving your points with those of the mail you're replying to works well.
Avoid jeopardy (or 'top') quoting, with the reply above the original content. Although this suggestion is more controversial (and hence less binding) than some of the others, this still annoys many people, so please think hard before doing so.
Do not use overlong signatures Keep them to within four lines, use the standard "-- \n" separator to mark the start of the sig, or both. (Some people have Evil Corporate Disclaimers they can't remove. These people are, however, still able to use the standard sig separator; please do so.)
If posting a job-related email, either looking for an applicant or letting people know you're available for work, please put [JOB] in the subject line of your email, so people who dislike job-related emails can filter them out easily.
Mark spoilers for film or television series in the subject line, and include suitable 'spoiler space' (usually a very minimum of 20 blank lines) before your content. This particular rule is especially important for long-running series that members of London.pm like, for example Buffy the Vampire Slayer.
TV series are considered to be OK to post unspoiled a day or two after their UK terrestrial showings. (There's an extra day or two to allow TiVo users to view their recordings.) Films are harder to set hard and fast rules for, but in the past a month or so seems to have been sufficient. However, adding space never hurts.
Yes, there are public archives on this site.
If you don't want your content publicly archived, the archiver respects "X-No-Archive: yes" or "Restrict: no-external-archive" mail headers so if you have a mail client that allows you to add headers you can try that.
A lot more than post.
Subscribers can get a list of members. This is left as an exercise for the reader.