Hello & welcome to the forum.
As main.cf is rewritten by Zimbra each 30 minutes, you should not do any changes to it (see here :
Zimbra MTA - ZimbraWiki).
Instead, you should add your changes to /opt/zimbra/conf/zmmta.cf
Anyway, there's no need to change any of these files as the RBL parameter are kept in the LDAP (as you used the zmprov command to add them to the MTA configuration) : using zmprov like you did is the "Zimbra way" to add the line in the main.cf file (as documented by TrendMicro).
Oh, and you should upgrade.
Really.