Because one cannot rotate ads
in an e-mail/newsletter zone it works correctly only with one active banner linked to the zone at the time.
However currently UI allows to have more than one active banner linked.
It should be fixed so that:
- it does not allow to link campaigns which dates overlap
- it does not allow to link more than one banner from active campaign [linked banner should be unlinked first OR linking another banner should automatically unlink the linked one]
- it does not allow to change campaign date if its banner is linked to newsletter zone and new dates will overlap with other campaigns linked to the zone [or it could automatically unlink the edited campaign with appropriate warning]
The only way in which a newsletter/email zone can have more than one banner linked to it is:
- when banners come from different campaigns and campaigns' activity periods don't overlap
In this case, a banner would be displayed only from the currently activated campaign