A form that has stopped emailing you feels like a form that has stopped working, and the instinct is to rebuild it. Resist that for a few minutes, because the two are rarely the same thing. Storing a submission and announcing it are separate steps, and only one of them depends on the internet's least reliable system.
Work down this list in order. The first check settles the question of whether anything is actually lost, and most people stop there.
1. Separate the entry from the email
Open the form's submissions list and look at the most recent entries. If the ones you never heard about are sitting there, the form is fine, the data is safe, and you have an email delivery problem rather than a form problem. That is a much smaller thing to fix and it changes what you do next.
If the entries are genuinely absent, skip to the last two sections — the submission is failing before it ever reaches you.
2. The mail is in spam, and has been for a while
Check the junk folder, and check it in the actual mailbox rather than in a forwarded copy. Then check any rule or filter you have set up: a tidy-inbox rule written months ago that files anything containing the word form into an archive folder is a classic, and it is invisible until you go looking.
If you use a shared address such as info@ or hello@ that several people read, check whether someone else has been filing them. More than once the answer has been that a colleague has been handling every enquiry quietly for weeks.
Mark a few as not spam. That teaches your own mailbox but does nothing for anyone else's, which is why the DNS section below matters more than it looks.
3. The notification address is not the one you think
Notification addresses are set once, during setup, and then never looked at again. Check the exact address the form is configured to notify. Common findings: a personal address from before the business had a domain, a staff address belonging to someone who has left, a typo in the domain, or an alias that forwards to a mailbox nobody opens.
Also check whether the notification is being sent from the same address it is being sent to. Several mail providers treat a message that claims to be from you, to you, sent by a third party, with deep suspicion, and some discard it silently.
4. Your domain does not authorise the sender
This is the cause that produces the most confusing symptom, because the mail is genuinely being sent and genuinely being rejected or quarantined, and nothing in your form tool reports it.
If notifications are sent as your own domain by a service running on someone else's servers, receiving mail servers check three records before they trust it. SPF lists which servers may send as you. DKIM is a signature proving the message was not altered and came from an authorised sender. DMARC tells receivers what to do when the first two fail. If your form provider is not covered by those records, strict receivers will quarantine the message, and Gmail and Outlook have both tightened this considerably.
You have two honest options. Add the sending service to your SPF record and publish its DKIM key, which is the right fix and takes a DNS edit. Or stop sending as your own domain: let the notification come from the tool's verified address with the enquirer set as the reply-to, so hitting reply still works.
5. The form never actually submitted
If entries are missing from the dashboard too, the submission is failing in the browser. The usual cause is a required field that fails validation in a way only some people hit — a phone field that rejects an international format, a date picker that behaves differently on mobile, a field that became required after launch and is now blocking an otherwise finished form.
You will not find this by testing the form yourself, because you fill it in the way it expects. Test it the way a stranger would: on a phone, on mobile data, in whatever browser you never use, leaving an optional-looking field blank, pasting a number with a country code in front of it.
File uploads deserve their own check. A size limit that rejects a photo straight off a modern phone camera will stop a submission dead, and the message shown is often vague enough that the visitor simply gives up.
6. The test that settles it
Submit the form yourself from a phone, on mobile data, signed out, using an address at a different provider from your own — a personal Gmail if your business runs on Outlook, or the reverse. Then look at three places in this order: the submissions list, your inbox, your spam folder.
Entry present and mail in spam means a deliverability problem, and section four is your fix. Entry present and no mail anywhere means the notification address or the sender configuration. No entry at all means the form itself, and section five is where to look. Each of those is a different repair, and guessing between them is how an afternoon disappears.
A note on what you can control
Email will always be the fragile half of a form. You cannot make another company's spam filter behave, and you will not get a report when it decides against you. What you can control is whether a lost email also means a lost enquiry.
Use a form that stores every submission independently of the notification, shows you the entries in one place, and lets you export them. Then a filtering problem costs you a delay instead of a customer. OneSol's forms store every entry and let Sol AI build the form itself from a sentence describing what you need to collect, so the data is in one place whatever the mail does.