When recipient doesn't receive your mail in HTML format and see plain text
If you are able to send and receive mails in HTML format then issue might be at the recipient end. How the message appears to the person receiving it depends on their email program. If the recipient's email program is set to convert messages, then a message you send formatted as HTML could be converted to plain text. Please ensure the below settings are set on Outlook. On the File tab, choose Options > Mail. Under Compose messages, in the Compose messages in this format list, click HTML Please ensure the below settings are set on Office365 OWA/Webmail. Log on to https://outlook.office.com/owa/ At the top of the page, select Settings (gear icon) > Options, and then select Settings > Mail Mail > Layout > Message format Compose messages in this format is set to HTML At the recipient end, check for the below settings in the Outlook application and try to disable Antivirus add-ins/scans. Click on File > Options > Trust Center...