Ironically, I tried to do my MIL a favour and use her double up Sainsburys voucher before it runs out. Had to queue at Customer Services for 10 minutes as computer said no and they took her Nectar card hostage until I sorted it. Always joked at work that my motto is now Never do anything for...
That would be the Outlook software. He has an Outlook email account which is different. I'm going shopping so hopefully someone more patience will get involved with what a mail client is an how it works in this instance.
You have been given the answer twice on this thread by others. You need an email client such as Thunderbird which will download the emails onto your PC. If you really want them on USB after that then you can.
20 years ago, I did have a guy at work who got upset that all of his saved emails had disappeared. He had been using his recycling bin for storing all the important emails he wanted to keep.
If he downloads using Outlook then he has a local copy anyway making it moot. Maybe if it is setup as POP without a local cached copy then this would work. Regardless, it will need someone with the patience of Job to get to the bottom of it.
Edit - he says Outlook account - not Outlook so my...
Funny as it would be to have him do it and then lose everything - you are wrong. A folder on your cloud based email is still in the cloud. You need them downloaded to a mail client. But I am damned if I am giving him any more free support.