I'd also like to see Windows 10 default Mail client in previews.
:) Well, I guess you are right. I have to get my eyes checked I think.
Sorry, Outlook desktop programs, NOT Outlook.com.
OK, with some help from my friends from Stack Exchange, this is solved.
The way to solve this is similar to the way we add pre-header text everywhere else - it just needs to be Outlook specific.
This solved it for me:
<div style="font-size: 1px; line-height: 1px; display: none !important; mso-hide: all;">Add pre-header text here. Make sure you have a lot of text since the default Outlook 365 preview is 3 lines.</div>
Lucy, you solved my issue! Thanks a lot!
Fantastic! This just saved me a few hours.