trigger for more than one host

[sg42]

Hi!

Can I somehow 'summarize' the items of different hosts in to one trigger?

Example1: we have multiple smtp Server which are not always in service. We
only want to trigger an 'Service Down' when all servers are down.
Example2: we have a couple of Switches where we looking at the broadcast
traffic. When there is an error, all items shows the same problem, so
we want only one notification, not one for every switch.

TIA,

Stephan

[sg42]

Update: I've found the thread https://www.zabbix.com/forum/showthread.php?t=51332 which quite adresses example1.
Where will aggegrate checks be defined? Have I to create a separate host?