This article is based on material authored by members of the news.newusers.questions Moderation Board and nnq-workers mailing list, particularly by Kathy Cole (until 2005) and Thor Kottelin (since 2007).
HTML-formatted postings are not welcomed in newsgroups. While your software may interpret HTML correctly, many newsreading clients have only minimal ability to correctly display HTML. Also, HTML postings often include your message twice: a plain text version is followed immediately by a version including HTML tags. This extra version of your message more than doubles the total length of the posting, and adds unnecessary download time for other newsgroup readers. Between other users' software's inability to correctly interpret your posting, and the longer postings costing additional money to download (much of the world uses dial-up connections, but doesn't have free local calling), you're likely to receive complaints if you post in HTML. These complaints can range from polite to thermonuclear.
If you're using Netscape Navigator/Communicator or Microsoft ® Internet News/Outlook Express to read and post news articles, you're affected. What may seem to you like a plain text message could actually be posted in HTML without you realizing it, because of the way those software packages are designed.
If you're using Netscape Collabra 4.x or Microsoft ® Outlook Express and you post with vCards, you will likely also get requests to stop doing so. For those using other newsreaders, vCards just look like a really long signature, which newsgroup readers commonly find annoying.