Outlook only sometimes turns emails to plaintext

WMaltman 

The issue you're experiencing with Outlook occasionally converting emails to plaintext and attaching a winmail.dat file can be caused by various factors. Here are some possible causes and solutions you can try:

1. Incompatible email client: If the recipient is using an email client that doesn't support HTML formatting or rich text, Outlook may automatically convert the email to plaintext. In this case, ask the recipient to check their email client settings or try sending the email in a different format, such as plain text or RTF (Rich Text Format).
2. Outlook settings: Check your Outlook settings to ensure that you are composing and sending emails in the desired format (HTML). You can do this by going to File > Options > Mail > Compose messages and selecting "HTML" as the default format.
3. Exchange Server settings: If you are using an Exchange Server, the server's settings might be causing the conversion to plaintext. Contact your Exchange Server administrator to check if there are any specific settings that could be causing this issue.
4. Signature or message format conflicts: If you have a signature that contains incompatible formatting or if there is a conflict between your message format and the recipient's preferences, it can trigger the conversion to plaintext. Try temporarily disabling your signature and ensure that your message format aligns with the recipient's preferences.
5. Antivirus or security software: Certain antivirus or security software can interfere with email formatting and cause the conversion to plaintext. Temporarily disabling or adjusting the settings of your antivirus or security software can help determine if it is the cause of the issue.
6. Corrupted Outlook profile: If the issue persists, it could be due to a corrupted Outlook profile. Try creating a new Outlook profile and see if the problem occurs with the new profile. If not, you can consider migrating your data to the new profile.

If none of the above solutions resolve the issue, it may be helpful to gather more information about the specific circumstances when the issue occurs (e.g., specific email content, recipient email client, outlook version, operating system, etc.)