Outlook - How To Send As Another Email Address

Classic Outlook

Open a New Email.

Select the Options Tab.

Select From in the Show Fields section. This will add the From field to your email.
 

Select the From Drop-Down Menu above the To field.

Select Other Email Address.
 

Select From.
 

Select More Columns.

Ensure the Global Address List is selected in the drop-down menu.

Search for the Email Address you wish to send from.
NOTE: You will need to ensure you have access to send from that email address.

Select Ok.
 

Select Ok.
 

Continue Entering the rest of your email.

New Outlook

Click on Settings (cog wheel top right) --> Email --> Compose and reply and tick the 'Always show From' box then Save

Click New email Then click on the From dropdown box --> Other email address...

Type the email address in the text box and then click on the mailbox you want to send from

After that, the mailbox should then appear automatically as a previously used address for the next time you need to Send As a particular address