I don't think you will find too many Incredimail users here.

You are probably better off researching conversion to Thunderbird or Outlook and use that as a stepping stone in the first instance.

There will be advice available in the archives of this forum in relation to conversion from those programs.

A method that does work, but can be painfully slow, is to create an IMAP account with a free provider and (assuming Incredimail can handle IMAP)

move your messages to the IMAP folders and then open that account in Pmail. You can then transfer your messages to local folders.

My Dad uses incredimail and is having an issue where downloaded email does not get cleared from the server, even though the options say not to keep a copy on the server. It is inconsistent but it seems that it depends on the volume of email in the inbox on the server. I have tested with Pegasus (which I use) and it does not have the same issue at all. Is there a way to convert incredimail files to Pegasus so he can change clients?