This problem can also occur in other situations. This problem can occur if one or more of the following conditions are true:
- In the File > Options > Mail dialog box, the Compose messages in this format option is set to Plain Text.
- You are replying to or forwarding an email message that you received in plain text format. Outlook uses the format of the original message in a reply, even if the Compose messages in this format option is set to HTML.
- You manually change the format of the message to Plain Text.
- The message that has the attachment is generated by another program that uses Simple MAPI to create the message.
- You are sending a file from Windows Explorer or another file management program by right-clicking the file, pointing to Send to, and then clicking Mail recipient.
- Open any Office application, such as Outlook or Word.
- Click File, and then click Office Account or Account.
- View the Version that is listed under Office Updates.
- If the version is not at 16.0.6366.2056 or a later version, click Update Options, and then click Update Now.