Yes, Lyris comes with a program, named "imp-arc.pl" to do this.
The program will import "standard mail archives". This is the mail archive format that Unix mail creates, and many other platforms create this format as well.
Each message is stored one after another in a file, with a "From " line separating each messages. You can import as many mail files as you have.
The messages will be full text indexed and appear in Lyris as old messages, as if they had been created in Lyris. They can be searched from the Lyris Web Interface as well as by email.