Email systems apply attachment limits to the encoded message, not only the file displayed in Finder or File Explorer. Leave sensible headroom instead of compressing to the exact published maximum.

The right level depends on the document: photographs tolerate different settings from diagrams, fine print and scanned signatures.

Start with the delivery requirement

Check the recipient’s stated limit and target a file comfortably below it. If several attachments share the message, budget for all of them rather than treating each in isolation.

Compress once from the original

Use the quality-first level, download the result and inspect small text at 200% zoom. Move to a stronger level only when the file remains too large. Recompressing an already compressed copy can multiply artifacts.

  • Keep the original untouched.
  • Check the largest image-heavy pages.
  • Confirm text remains searchable.

Use a link when quality matters more

If readable output cannot fit safely, use an organization-approved sharing link instead of destroying detail. Password protection can control opening, but share the password separately.