Hi VM_Expert
Why don't you change the vCenter Server settings Mail Sender adress?
You can just select the Mail Sender address on the vCenter server settings.
MAIL then you will have the Mail server defined
Underneath you can define the Mail from Adress, define for vCenter 1 vCenterA and for vCenter 2 vCenterB or whatever name you will use.
Then it will send it from those names, therefore you know then which vCenter is alarming.
Best regards,
Marco