Setting to 0 would send an out-of-office notification in response to every email received. (Default is 7 days.)
Thus duplicate away messages will not be sent to the same user in the given interval of x days. On day x+1, if they send that account an email, they would again get back another notification.
CLI would be:
zmprov mc COSname zimbraPrefOutOfOfficeCacheDuration 0
zmprov mc COSname2 zimbraPrefOutOfOfficeCacheDuration 1d
or:
zmprov ma
user@domain.com zimbraPrefOutOfOfficeCacheDuration 0
zmprov ma
user2@domain.com zimbraPrefOutOfOfficeCacheDuration 1d