Sub folder delayed mail recieve in Outlook 2010

Please, I use Outlook 2010 with 7 email accounts set up in it. I am able to fetch mails from all senders into my main folders and subfolders in Outlook, except for one subfolder created for mails from a particular colleague of mine. I see number of unread mails besides this subfolder, but I am unable to receive the mails until it is exactly 12 midnight each day.

Meanwhile, I am able to receive his mail in a timely manner without issues on all other devices that I use such as my iPad, HTC Windows Phone, etc.

I have checked rules just in case I mistakenly created a rule to delay his mails, but there is no such rule. It is also important to note that for the past 6 years I had always received his mail timely without issues, until a few months ago when I noticed the problem started.

Please, any similar experiences, or an idea of how I can solve this annoying problem?

Thank you Ranger4.

Yes, I have checked the IP settings. To also confirm that is not the problem, I receive mails without delays from other colleagues who are on the same domain as the guy whose emails I have delays with. We are all in the same small office, and I set up each person Outlook, being the owner of the business, and the IT administrator.