Self-promotion is allowed on 3D-PRO — using the PLUG: subject header key — but care should be given to not over-promote.
It is perfectly acceptable to share timely information with regard to your projects, services, or promotions — as a means to benefit and/or inform list members — but it should not be used as part of your marketing strategy. And it should not take the place of what would typically go in a company newsletter. Do not repeatedly post PLUGS at a frequency that makes it feel like a marketing campaign and not real and/or important news.
While there are no set numbers with regard to what is considered an acceptable amount of self-promotion, once per month may be borderline too often. Much of it depends on how your posts come across.
It is also ok to mention your products or services if it is intended to be informative and helpful and fits the context of conversations, but 3D-PRO is not the place to for specifically marketing your products to people out-of-context.
When in doubt about using the list to gain or put exposure on something, simply send me an email regarding whatever you are thinking about posting. I’m usually pretty quick to respond and getting the okay to post your plug or announcement will give you immunity in the event anyone complains.