This page only applies if you are using an email client checking email via a POP email server.
For Email Forwarding to work, you need to leave a copy of the message on your POP server when checking with your email client.
If this is not done, your email client may check new mail and remove it from the server before VersaForward gets a chance to see it.
The result of that would be some messages forward while others do not.
This can be easily fixed by telling your email client to not remove the message from the POP server immediately.
All email clients have this feature and some of the more popular examples are listed below.

Go to your account Server Settings. Select
Leave messages on server and then enter the number of days you'd like to keep a message on the server before removal.

Open Accounts from the Tools menu and select your account. Go to the Advanced tab.
Select
Leave a copy of messages on server and then enter the number of days you'd like to keep a message on the server before removal.