I suggest you to archive the e-mail account folder using the command
Code:
tar -zcpf account.tar.gz account
where account is the e-mail account's folder name. The archive account.tar.gz can be uploaded to the destination server and unpacked using the command
Code:
tar -zxpf account.tar.gz
Please, note, that this operation should be done in /home/username/mail/domain.com/ folder.