You can use migration tools because IncrediMail doesn't have an Export feature nor there are application to offer custom migration to other email clients. There is one, though, that helps you migrate to Outlook, but that's it. To move the email from IncrediMail to another email client, you will need to save the emails as .eml file format then drag and drop the .eml file to the other client.
To save the EML file, go to File > Save As and save the email with a name of choice.
Repeat the steps above for each email you want to move to another email client's Inbox folder.
To find more information about it, access the official website.