To edit an auto responder or out of office message, you first need to log into your 123-reg control panel, then follow the instructions below:
Scroll down the page until you reach the Email section.
Click on the Manage email link.
Find the mailbox that you wish to set up an auto responder on under the Email Address section by selecting the relevant domain name from the drop down box.
Hover over the More button of the email address you wish to set the auto responder on.
Select Auto responder from the list that appears.
Select the ON button, enter your message and press the Save & Exit button to complete the setup.