It was relatively painless process.
I have over the years used several e-mail programs – Outlook Express, Thunderbird, Bat and Barka. It was easy to immigrate from OE to Thunderbird and again to TheBat that was perhaps the most powerful of them all. Unfortunately, it is against HTML-formatting so I moved on to Barca that in many ways was ideal for my purpose with one exception, it was unable under certain conditions to render my national character set (Danish) correctly. The development of Barca/Poco has now stopped so I have as a last resortturned to Outlook (2010) and I wanted to import my messages from TheBat and Barca and close those chapters. Outlook Import Wizard seemed to be the only solution. It was relatively painless to import from TheBat, probably a result of the design philosophy of the developers, but Barca required using the Mbox converter. I imported more than 50,000 messages and all were correct (!).