Bullet points have had huge inconsistencies with recent versions Outlook.
Prior to Outlook 2007 all versions of Outlook rendered standard bullet points pretty much perfectly and pretty much the same as any other email client. With Outlook 2007 however they introduced the Word render engine to Outlook. This removed much of its previous standards compliance with its own proprietary code.
This unfortunately means bullet points amongst many other previously fine email elements were now messed up in Outlook 2007 onwards. There was great outcry from developers and users at the time but it fell on deaf ears and the flaws in Microsofts Outlook renderer have persisted pretty much unchanged up to the present day.
Developers have found hacks and other creative but not always easy ways around many of them however bullet points is one that is not really fixable. Fixes tend to work only one or two versions of Outlook and make things worse in others or in more standards compliant Email apps.
The only way we have found to remedy this is to use the table method I previously linked to. Constructing your bullet points in complex tables. However this is something not for the faint hearted!! It’s tricky to do and a nightmare of you are using it in a template that is repeatedly reused. Its best used when in a unique single use template.
I don’t think it’s suited as a method for use by anyone without in-depth HTML/CSS know-how either.