Steps to add Email Signature in Outlook
Open the Outlook Web app: https://outlook.office365.com/mail/inbox and go to settings page
Shortcut to Settings page: https://outlook.office365.com/mail/options/mail/messageContent
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Step 1: Click the Gear Icon to Open Settings
This opens right hand sidebar, towards the bottom Click > View all Outlook Settings
Step 2: Click > Compose and Reply
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The first option available is to add email signature
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Write/Paste your signature and press Save
Check the box for – Automatically include my signature on messages I compose