The auto-reply function in Outlook has some restrictions. The reasons that your colleague did not get a reply may be due to the followings:

1. You have a preferred name in the Address Book. The sender will not get an auto-reply message if he sent mail using your preferred name.
2. This is not the first time the sender sent you a message while you are out. The sender will only get that the first time he sent a message to you.

There is a get around (though a bit complicated) for the above in case you would like the sender gets a reply when he sends a message using either your full name or your preferred name and will get the reply every time a message is sent to you while you are out. Follow the steps:

1. On the Tools menu, click Out of Office Assistant.
2. Click I am currently Out of the Office.
3. Then click the Add Rule button to open an Edit Rule dialog box.
4. Under When a message arrives that meet the following conditions, type both your e-mail full name (e.g. Chan, Mei PO) and the preferred name (e.g. May Chan) in the Sent To text box. It makes the server send the reply to all the users sending message to you, no matter they use your full name or your preferred name in the To: field of the incoming message. Keep the From field empty if you want this rule apply to all senders.
5. Under Perform these actions, select Reply with, and click Template button to open a Reply Template dialog box.
6. Type the message and the subject of the reply message you want to reply to the senders in the box. Click the Save button and close the Reply Template dialog box.
7. Click OK to leave the Edit Rule dialog box. Click Yes when the dialog box with warning written This rule will fire for all incoming messages. Is it what you want? appear. Then there will be a new rule appears in the These rules will be applied to incoming messages while you are out of the office box.
8. Click OK to leave the Out of Office Assistant dialog box.

Note:

1. Rules in the Out of Office Assistant dialog box are applied in the order they appear from top to bottom.
2. If you have more than one condition in the Edit Rule dialog box, only messages that meet all of the conditions will get the reply message.