If you need to edit a table in an Outlook signature with adding borders and backgrounds, please do as follows:

1. In the Mail view, click Home > New Email to create a new email.

2. In the new Message window, click Insert > Signature, and select the specified signature whose table you want to edit. See screenshot:

3. Now the signature is inserted into the message body. Please edit it as follows:

A. Add border for an Outlook signature

Select the whole table in the inserted signature, and then click Design > Borders > All borders or other options to add border for the table.

Note: To add custom borders for the table, you can (1) specify the border style by Design > Border Style, (2) configure border color by Design > Pen color, (3) set border width by Design > Line Weight separately, and then (4) click Design > Borders > All borders.

B. Add background color for an Outlook signature

Select the table in the inserted signature, and click Design > Shading, and then specify a background color from the drop down list. See screenshot:

4. Copy the whole signature content in the message body, and click Insert > Signature > Signatures to open the Signatures and Stationery dialog box.

5. In the Signatures and Stationery dialog box, go to the E-mail Signature tab and:
(1) Select the specified signature whose table you will change in the Select signature to edit list box;
(2) Clear all content in the Edit signature box, and then paste the signature copied from message body;
(3) Click the OK button.

So far, you have added borders and background for the table in the specified signature. Please close the new email without saving.

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