Make every submission trustworthy.

Validate at two boundaries

The client should explain errors quickly, but the backend must enforce the actual limits. Validate length, format, allowed values and file size or type before accepting a submission.

File upload checklist

The list below breaks this down into the parts that matter most. Read through each one and note anything that applies to your own setup.

• Limit file size and accepted MIME types.
• Generate a safe object path instead of trusting a filename.
• Keep private uploads in a protected bucket.
• Save the upload reference with the related form record.
• Delete abandoned or replaced files deliberately.

Email delivery

Follow the sequence below from start to finish. The order matters: later steps assume the earlier ones are done.

1. Persist the form record before attempting notification delivery.
2. Send only the fields the recipient needs.
3. Use a verified sending domain and a clear From identity.
4. Record delivery status without exposing provider secrets.
5. Provide a retry or queue path for temporary failures.

Privacy

Only collect files and personal information that the stated purpose requires. Tell visitors how the submission is used and provide a route to request help with their data.

Examples of validation worth enforcing

Before making changes, work through the points below. Each one covers a different part of the picture, so treat them as a set rather than picking favourites.

• Reject files above the agreed size limit with a message stating the actual limit, not a generic error.
• Reject file types outside an explicit allow list rather than blocking a deny list, since deny lists miss variants.
• Cap free-text fields at a sensible length so a single submission cannot exhaust storage or notification quotas.
• Require a valid format for email and phone fields before accepting the submission.
• Strip or reject unexpected fields in the payload rather than silently storing them.

Handover checklist for a launched form

A few moving parts are involved here. The points below cover each of them, so you can see the full scope before deciding where to start.

• Document which fields are required, their limits and where the data lands.
• Confirm who receives the email notification and what to do if it stops arriving.
• Confirm storage bucket permissions match the sensitivity of the uploaded files.
• Note the retry or manual resend path for a failed notification.
• Set a reminder to review and delete stale uploaded files on a schedule.

Frequently asked questions