How to import data from old Thunderbird into eM Client?
eM Client does not have integrated solutions to import data directly from Thunderbird, and Thunderbird has no native option to export its e-mails.
However, there is a Thunderbird extension called SmartSave which can export emails from Thunderbird to eml files. You can find the extension here.
Alternatively, you may also use a stand alone program such as mbox2eml which can convert Thunderbird’s data files- mbox files into standard eml files.
Once you have all your emails in .eml format you can import them into eM Client by selecting from the Main Menu: File -> Import… and then Import from folder with .eml files.
Thunderbird’s address book does contain an option to export its contacts in the form of LDIF files which however is not a standard format for storing address books. Hence you need a third party program to convert LDIF files into the standard vcf files (there are many online tools for this purpose). Once the contacts are parsed into vcf files, you can easily import them into eM Client by selecting from the Main Menu: File -> Import… and then Import contact from VCard (.vcf).