The formatting of your email container is controlled by your forum's DEFAULT style, in the Style Editor. Its in the "Email Properties" group.
You could design your email "guts" template in a third-party HTML editor, such as Adobe Dreamweaver or a Mail Manager program, and then populate the subject and contents as needed, before sending out through UBB.threads
. Though, its more advisable to use a dedicated Mail Manager for doing such things, as that provides a direct option for the reader to unsubscribe themselves. The dedicated mailer would maintain its own list of emails that dont want to have anything sent to them. Doing this means that when you export all the emails from your query to a list for importing to the Mail Manager, That Mail Manager will exclude everyone that had opted out. Theoretically. Though, Im not sure how that third-party program would keep track of re-subscribers. Thats beyond my experience with the proposed UBBT/Export => Mailer/Import setup at the time of this post.
Attached are a few screenshots of the extent of the current mailer search/select/send pages. Its all pretty basic stuff. Stuff for just sending out general emails to users who want to have communication from the forum.
There is one more page which contains search results, but I dont have a "clean" sample screenshot of that, which doesnt also display personal information such as login dates, email and IP addresses.