Have you recently upgraded to IBM Notes 9? Then you may also have noticed that any Rich Text tables are being received by Outlook users with visible borders.
Our developers have discovered that it is a bug in the new IBM Notes 9 HTML conversion process:
It looks as though a fix is being tested for the upcoming IBM Notes 9.0.1 release.
Our current work around is to use the new 'Advanced Customised HTML' feature to modify the generated HTML. You will need to remove the following attribute from any < TD > tags: style="border-style:solid;border-color:#000000;border-width:0px 0px 0px 0px;padding:0px 0px;".
Please contact firstname.lastname@example.org if you have any queries.