I currently use this standard for all email superscripted numbers, reg marks, etc:
<sup style=“font-size:10px;line-height: 0;”> adjusting font-size accordingly, and it seems to render beautifully in all email clients EXCEPT Outlook 07/10. In Outlook, the superscripts are often extremely tiny and lower when compared to all other clients.
After googling a bit, I found this suggestion:
<sup style=“font-size:.90em;line-height: 0;vertical-align:super;”>
which made superscripts slightly larger and slightly higher in Outlook, but also made them much larger and higher in every other client.
Is there a better compromise between the two to make superscript size and placement a little more consistent between outlook and the other clients?