You're using word as the editor and it’s a word feature.

(--- and ____
also do it - 3 of the character cause this paragraph underlining. )
If you hit Ctrl+Z as soon as it changes, it should undo. To disable, go to
tools, options, spelling tab, autocorrect options - Autoformat as you type
tab - Border lines option.
--
Diane Poremsky [MVP - Outlook]
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"Your Display Name here..." <(E-Mail Removed)>
wrote in message news

3BE2250-562F-438B-924E-(E-Mail Removed)...
> If you type ==== and then return, outlook puts in a double line.
> This object:
> =========
> Cannot be selected.
> Cannot be formatted.
> Cannot be deleted.
> It is NOT a border.
> Turning borders off simply moves the line.
> Selecting all text before and after and hitting delete moves the line.
> It is not under AutoCorrect.
> It is not under AutoFormat.
>