Emails from redmine should include headers that don't trigger vacation auto-responders
I'm afraid the fix proposed in #2879 doesn't work for Outlook/Exchange. My apologies for not doing enough research! Ticket 5288 in the trac project, and the end of this post on the MS Exchange Team blog suggest that adding:
...to outbound emails will do the trick.
(I haven't re-opened #2879 since the subject line would have been misleading).