Emails Don't Move to Outlook

Win Me/Outlook 2002/NOD32 AV/No Firewall - - A daily, typical scenario: 2 emails from Trusted Sources (5K/12K) wouldn't move this a.m. to Outlook; All I did was open the Bellsouth ISP Email site to see the messages, Clk'd Outlook Send-Rec again, and they moved over. Sometimes I Delete Spam emails in the group, then they move. A prior post answer suggested a non-standard preamble data string on some emails may cause the hangup until those emails are removed but only 2 Regular, Trusted Senders were involved here. Are there any other ideas as to why emails [often] don't readily move over to Outlook? Thanks!