Set a List-ID header on all emails. This can help with filtering in email clients. It will also stop most auto-responders from sending replies back to the sender (out-of-office, on-vacation, etc.).
You can use whatever name and id you want, but the format should be similar to one of the following (including the < and > signs around the actual id):
<ci-notifications.company.org>
Build Notifications <ci-notifications.company.org>
"Build Notifications" <ci-notifications.company.org>