Compress JPG for Email

Gmail and Outlook both advertise a 25 MB attachment limit, but that figure is the size of the encoded message rather than the sum of your files. Attachments are transmitted as base64, which inflates binary data by roughly 33%, so the practical ceiling is closer to 18–19 MB of actual photos. A dozen untouched phone pictures will exceed it.

The receiving server matters more than the sending one, and it is the stricter of the two that decides. Plenty of corporate mail systems cap inbound messages at 10 MB, and some older systems at 5 MB. A message that leaves your outbox successfully can still bounce hours later, which is why sizing photos down before sending is more reliable than discovering the limit afterwards.

This preset caps the longest edge at 1600 pixels and targets roughly 300 KB per photo. At that size an image still fills a laptop screen when opened and prints acceptably at postcard size, while roughly fifty of them fit inside a 19 MB envelope. It is the balance point where the recipient sees a real photograph rather than a thumbnail and the message actually arrives.

For photographs the recipient intends to print large, or that will be edited further, send the originals through a file-sharing link instead. Compression for email is a delivery compromise: it optimises for the message getting through, and the discarded detail is not recoverable from the attachment afterwards.