Hi @bertram12 ,
But when someone replies to my email, the vertical spacing in my original message has become huge.
Do all the reply messages that you received display the abnormal format? If the issue only happened to some specific messages, are there any similarities of them (same recipient or other similarities)?
Also, if you send a message to yourself and reply it, could the format of this message display normally?
I have tried to test in my Outlook 365 and Outlook 2016, according to my tests, the vertical spacing wouldn't be changed if I sent a message to other users in my organization and they replied to me in Outlook. However, if I send to the Gmail users and they replied to me through the web mail, the spacing of the new message turned to "auto", which is same with your issue.
Can anyone tell me why Outlook is changing my "Before" and "After" settings to "Auto"?
I also have researched a lot about it, and found it may be caused by the HTML coding and depend on the way Outlook creates line breaks in HTML and how browsers or other clients interpret them, for more information, you can refer to this article:Messages are Double Spaced for the Recipient. (Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
how can I change it?
Actually, the format of these replied messages that your received from others wouldn't be affected by your setting, it's more related to the recipient, so it's suggested to contact the recipient to change the format of message or other operations as the article mentioned above and reply it to test.
Hope this could be helpful to you.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.