Attachment too large and format not allowed are common reasons homework and office email fail. Prepare to the receiver’s rules early.
Learn the rules
Check the per-file size limit, whether multiple attachments are allowed, PDF versus images, and whether Chinese filenames work on the portal.
Prefer short names without odd symbols, for example name-course-hw01.pdf.
In the message body, say what the attachment is and how many files you sent, so it is clear on a phone too.
Ways to shrink files
Many photos: compress or resize, then Images to PDF. Many PDFs: merge into one if allowed. One huge PDF: try PDF Compress, or split to the pages you need.
Still over the limit? Ask about a drive link, and check permissions and expiry. Or split across messages and say how many parts in the body.
Open the attachment yourself before sending. Check scan orientation and missing pages.
Always compress from the original. Do not squeeze an already blurry sent copy again.
These steps run in your local browser and are not uploaded to our servers. Before you hit send, confirm the recipient and the right file version.