When you send an e-mail from a shared mailbox, make sure you check the address the e-mail is being sent from. It may well default to sending the mail from your account, rather than the shared account.
To see the account it is being sent from click the ellipsis (…) and click Show From
|Click From to change who the e-mail is sent from|
|Click other email address…|
Begin to type the e-mail address you want to send this e-mail from
Select the address you want to use from the suggested e-mails that will populate the drop down list
|Continue and send the e-mail as normal.|