Note: Make sure you use Chrome or Firefox during the installation process.
Create your email signature on MySignature.io and follow these simple steps to install it in Outlook web:
After creating your email signature, click Save signature button under the signature preview.
Or, if you have saved your signature, find your signature on the Dashboard and click Install button.
Select the Outlook.com / Office 365 icon in the list of email clients, then click Copy to clipboard button.
Open your browser and log in to your Outlook.com.
Open Quick settings and choose View all Outlook settings at the bottom.
Settings will open up in the Mail tab (which we need). Then go to Compose and reply. The signature section will be right there.
Paste signature to the signature section.
Note: Please make sure to put the tick in two options under to make sure your signature will show up in your composed/forwarded/replied emails and choose HTML format for writing new messages.
Save changes by clicking Save button. Then close the settings window.
Compose a new email and see what the signature looks like there.