There are various possible reasons for this, usually to do with third party internet security software but they may also be associated with Windows TCP/IP or dial-up adapter issues. You may not have problems with other software, but that doesn't mean the problem is being caused by VPOP3.

1. Check if you have any email anti-virus software such as Symantec, McAfee or MailScan installed. These programs will process all email TCP/IP connections and scan the messages at that point. Often there are problems with these programs which can cause sending or receiving of messages to lock up.
2. Check for 'Internet Security' or Firewall software. Some of these will act in a similar way to the anti-virus software above and can cause problems with certain types of attachments.
3. Check with your ISP to see if they've had similar problems reported before. We've had reports of this problem where the ISP has been able to fix it 'over the phone' by telling you to change some specific settings.
4. Check for driver/firmware updates for your network card. If possible try changing the network card in the VPOP3 server for one of a different model/make. The rest of the network may work OK, but we see many cases where changing the network card will fix the problem even if it seems to be working OK for other applications.
5. On the Utilities → Misc Settings → Network Tweaks page in VPOP3, try changing the following settings one at a time:
   • Disable TCP/IP Nagle Algorithm
   • Set the 'TCP/IP' block sizes to 512 bytes
   • Set the 'Winsock Buffer' sizes to 512 bytes

The following methods used to be important for Windows 95/98/ME and NT, but are less so with newer versions of Windows.

1. Download MTUSpeed from http://www.mjs.u-net.com/home.htm or DrTCP from http://www.dslreports.com/drtcp. This allows you to change some TCP/IP configuration settings. You can try the 'Optimum settings' option, or set the MTU to '576'.
2. Go to the Utilities → Misc Settings page in VPOP3 and turn on POP3 the SMTP Connection.