How do I get that nice inline-quote indicator in Outlook 2010 when replying to emails?

1. Click the File tab

2. Choose Options from the left menu

3. Choose Mail from the left menu

4. Scroll down for Replies and Forwards

5. Choose your relevant options from the dropdown. I think what you're looking for is "Prefix each line of the original message"

To remove the existing prefix / blue bar, change message type to rich text and press Ctrl-Q (per @djp and @Alexander Amelkin; be sure to up-vote those comments below if this helps).

As the comments have noted is an issue with variant's answer, you can't add text into the reply if you use the "Prefix each line of the original message" feature.

This is what I'm doing that takes a bit more setup and a bit more work to use but is way more flexible. Note that I'm using Office 365 ProPlus

1. Double click on some text to highlight it then click on the Styles menu
2. Name your new style. Click the Modify button
3. Make sure the checkbox Add to the Styles gallery is checked.
4. Make sure the option Style for following paragraph: is set to ¶ Normal
5. Click the Format drop down then click on Border
6. Set a left border, with the color you want, and the width you want.
7. Keep clicking Ok until you're back to your e-mail

Now that you've got your reply text style created, just highlight text that you want to mark and apply the style to your replies. Of course, you can apply all kinds of other customization to the style as you see fit.

Following @chizou 's answer, these are the parameters I found working.

• Format Text > Styles > Create a style (New Style) or choose a style to modify (Modify style)

• Format > Paragraph > Indentation

  • Left, 0.1 cm

• Modify Style > Format > Border...

  • Color blue

  • Width 1 + 1/2

  • Click the left border button

  • Options > From text > Left, 4 pt

In case you want to write plain-text emails with some nicely formatted text quotes, quotefixmacro might be a solution. It automatically converts HTML mails to plain text mails and reformats the quotes nicely (in most cases)

Other than that, for Outlook 2017 and newer, following are the options to add > before each line:

Tools > Options > Preferences > E-mail Options... > On replies and forwards

• When replying to a message: "Prefix each line of the original message"
• When forwarding a message: "Include original message text" or "Prefix each line of the original message"
• Prefix each line with: "> "