I went and did a search on Gemini and got these recommendations
Mac Mail Settings for Exchange Compatibility
The most important step is configuring Apple Mail to use a Windows-friendly format, which helps prevent the creation of the problematic Mac-specific attachment metadata.
Always Insert Attachments at End:
In the Mail app, go to Edit > Attachments.
Ensure that Always Insert Attachments at End of Message has a checkmark next to it.
Why this helps: It forces attachments out of the message body, which is a common cause of embedding/viewing issues for Outlook users.
Send Windows-Friendly Attachments:
In the Mail app, open a new message window.
Click the Attach Files paperclip icon in the toolbar.
In the file selection window, click Options (if visible) or simply look for the checkbox at the bottom.
Check the box next to Send Windows-Friendly Attachments.
Use Plain Text Format (Optional but Effective):
When composing a new email, go to Format > Make Plain Text.
Why this helps: This eliminates all HTML/Rich Text formatting complexity, which often causes issues with how Outlook renders in-line content and attachments.
Best Practices for Attaching Files
Avoid Dragging into the Message Body: While convenient, dragging and dropping files into the text area of the email can cause Apple Mail to embed the file (especially images) in a way that Outlook sees as an un-savable inline element.
Best Method: Use the Attach Files paperclip icon, or drag the file below your signature/the last line of your message body.
Use Universal File Formats: Stick to widely compatible formats:
Documents: PDF, .docx (Word), .xlsx (Excel).
Images: JPEG or PNG.
Avoid: Proprietary or lesser-known file types.
Check File Size Limits: Exchange servers often have strict size limits (e.g., 25MB). If your attachment is very large, consider using Mail Drop (for files up to 5 GB via iCloud) or a shared cloud storage link (like OneDrive, Google Drive, or Dropbox) instead.
