From MozillaZine Knowledge Base

All of the programs to export Incredimail messages convert them to .EML files. Sometime in 2007 the format used by Incredimail to store messages changed. At this time, only one of the programs works with the latest version of Incredimail. If none of the programs work with your configuration you could manually export messages one at a time from Incredimail as .EML files using the "File -> Save As" command.

Thunderbird has a "File -> Open Saved Messages" command that will let you read a .EML message but it will not import/save it. You can use the ImportExportTools extension to import the .EML files as real messages. You could also drag and drop the .EML files to a open folder window within Outlook Express (while its running, not its directory in windows explorer), and then import the messages from Outlook Express using Tools-> Import.

If your Incredimail folders are corrupted you may not be able to recover everything by migrating to another email client. However, by using .EML messages as the intermediary you have a good chance of identifying what messages are corrupted and could try editing them with a text editor before importing them.

• The shareware program Incredimail Backup PRO 2 works with the latest version of Incredimail, and is supposedly fully functional for thirty days. However, it appears to have limits (like many programs do while in trial mode) on how many messages it will convert.

• IncrediConvert is the most well known solution, but doesn't work with the latest version of Incredimail. The author stated in 2007 they would update the program later that year. However, the authors web site now states the sources are lost and they have no plans to update the software unless paid to do so.

• The same author also wrote the IncrediMail to EML Converter 1.0 program. It also doesn't work with the latest version of Incredimail.

Normally another alternative would be to use a IMAP account to migrate the messages. However, Incredimail only supports downloading from a IMAP account so it doesn't make sense to sign up for a free IMAP account, create IMAP accounts in both Incredimail and Thunderbird, upload the messages to the server, and then download them using Thunderbird. Most email clients that support IMAP let you upload and download messages, and it normally gives you the best results.

You can export your address books in Incredimail by selecting the address book, File ->Export , and then export the addressbook using the .CSV format. You can import that using Tools -> Import -> Address books -> Text files.