The message_queue table column "from_address" does not always get populated. We should either make the EnqueueLetter parameter 'from_address' mandatory, or (preferably) derive the correct from address from the letter's branchcode. If the letter has no branchcode, I imagine we should use either the KohaAdminEmailAddress or the patron's home library's email address.
Per our previous conversations, it sounds like sometimes this field doesn't get populated because it is a digest, and items may be from multiple libraries. 1) The from address should be from whatever library signs the notification ([% branchname %]). 2) If the notice is a digest and not from any particular library, it should be from the patron's home library. This should also apply to [% branchname %] if used in the notice. 3) It should only use the KohaAdminEmailAddress if 1 & 2 can't supply an e-mail address.
We enabled digests for hold notices some time in January. It looks like the message_queue table does not have a 'from_address' in any of the messages sent with HOLDDGST as the type. Looking at Christopher's reply, I would agree with #2, that a digest notice should be sent by the patron's home library if it contains information from multiple libraries. (We are a consortium so this would be ideal, over using the KohaAdminEmailAddress).