Well, the same as my situation. Zimbra command "zmprov" is great to do this.
first , creat a txt file with all the alias as this format
aaa
name1@abc.com alias1@ttt.com
aaa
name2@abc.com alias2@ttt.com
aaa ...... .......
and then upload the txt files to your zimbra server
last,run the command as zimbra user:
zmprov -f file.txt
all the alias will import to your server .