What is your mail client?  Exchange (and Office 365) will support multiple proxy address, but usually there is only one "SendAs", which (usually) corresponds to the "PrimarySmtpAddress".  If so, you are right, your boss has a different address than she thinks.  Check the mail headers on a message sent by her.
--Joe  

________________________________________
From: LISTSERV Site Administrators' Forum <[log in to unmask]> on behalf of Pete Weiss <[log in to unmask]>
Sent: Friday, June 24, 2016 11:15 AM
To: [log in to unmask]
Subject: Re: List owner cannot post to list

On 6/24/2016 10:20, Perkins, Stephen wrote:
 I have a number of lists. My boss and I are listed as owners. For practical purposes, I am the primary owner and my boss is secondary. I’m going on vacation in a week and I’m trying to show my boss how the lists work. When we go to the software, she cannot post to the list. She can see the list but none of the links are active.

My guess (without further data) is that the posting address does NOT match the list-owner address; or perhaps the secondary list-owner address has been commented out.  Possibly the MUA is inserting a SENDER: different from the FROM:

Real data would be useful:

1) original list-definitions

2) bounced email


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