What does this mean exactly? Is his machine a mail server?
I used to know an engineer/scientists who only used a single laptop (linux) and it acted as his mail server. When he travelled he used dyndns (or some such thing) so that delayed mail would be delivered to his laptop. Could never get a straight answer about whether this worked all the time or not (whether he ended up missing emails).
I use Thunderbird with pop3 settings that ask remote mail server to delete messages once downloaded. Then authenticated SMTP account to send.
No big reason, just what I do.
Edit: I believe that my shell-account provider is deleting those messages once downloaded, and not copying them somewhere else, but I have no guarantee of that as pointed out lower in the tree from the parent post.
If the gentleman is using a mail server on his PC that would be interesting as you say.