How to shrink an iPhone photo for email.

Start with the requirement

Find the actual attachment limit.

Look for a number in the request you received. It may appear in an upload form, an email message, or a support article. Record both the maximum size and any format requirement. A limit of “under 5 MB,” for example, is different from an instruction to use a particular image format.

Do not assume that every email service has the same threshold. Apple’s Mail guidance says that if a file exceeds the maximum size allowed by your email account, Mail may offer Mail Drop. Apple also cautions that the recipient’s email app may have a smaller message-size limit. If the destination gives a limit, use that limit. If it does not, check with the sender or service rather than treating a smaller file as a guarantee of delivery.

Protect the original

Make a smaller copy, not a replacement.

Start with the photo you want to send and preserve the original. The copy is the version you adjust for the destination. Keeping the original avoids losing the best-quality version just because one email needs a smaller attachment.

With UnderLimit, choose an image, enter the exact maximum file size, and export a new JPEG copy. The app verifies that exported copy against the limit before you share it. The original remains untouched.

This is a product-scope statement, not a promise that a particular email provider, recipient, or upload form will accept the file. Check the destination’s other requirements too, including format, dimensions, and whether the limit applies to one attachment or the full message.

Send the intended file

Attach the verified copy.

After you have the smaller copy, open your email draft and attach that copy rather than the original. Apple’s iPhone guide confirms that a saved photo can be attached from the Photo Library in Mail. Before sending, check the attachment name and size one last time so you do not accidentally send the larger original.

If the email service rejects the message, read the rejection notice. It may identify a lower message limit or another requirement. Do not try to bypass an attachment or security policy. Use the allowed sending method, ask the recipient what they can accept, or choose another approved route.