This is a behavior that occurs based on how the From Address is selected at time of send. When an Outlook cached Address is selected, it can sometimes fail to persist when sending email through the PoliteMail Server. For this reason, it is best to choose your addresses from your Global Address list. This will assure that the addresses will persist and behave properly.
A cached email address is one that you can start to type and it pops up as a selection. When it shows up in the selection list, it will have an X to the right-hand side, that you can use to delete the address from memory (only). If you see the address with an X beside it, don’t select that address.
To set the “From” address from your Global Address List:
1. To change the From address, click on the From drop down and select Other Email Address at the bottom of the list.
2. In the next window click on the From button, this will bring up the Global Address List.
3. Type or select the email address needed and click OK
4. You will see the selected address, click OK
5. The From address will now be set in your message.
Note: If you are using Outlook 2016 and you cannot see your “From” address in your email message window, go to your Options tab and click on the “From” in the Show Fields section of the ribbon.