When sending email attachments, the most widely compatible formats are PDF for documents you don't want modified and widely-used office file types like DOCX (Microsoft Word) or XLSX (Microsoft Excel). PDF preserves layout and fonts perfectly across different devices and operating systems, while DOCX and XLSX allow recipients to easily edit content if needed. Universal formats like TXT (plain text) and standard image formats (JPEG, PNG) are also reliably viewable by almost everyone.

Use PDFs for formal documents like contracts, reports, or flyers where consistent appearance is critical. Send DOCX files for drafts, proposals, or collaborative documents where recipients may need to edit or provide tracked changes within Word. JPEG or PNG are ideal for photos and screenshots shared quickly, as these image types open in any email client or web browser without requiring specific software.

Key advantages are universality and accessibility, minimizing the risk that recipients can't open the file. Limitations include file size restrictions imposed by email providers and potential security concerns around executable formats (like EXE) which are often blocked. Choosing widely recognized formats ensures smoother communication and avoids frustrations for both sender and recipient. Where long-term archiving is needed, PDF/A offers enhanced stability.