Several different problems can look like a missing email. Check where the delivery stopped before changing DNS records or repeatedly requesting another copy.
Recipient routing and sender authentication are different
The recipient domain's MX records identify where incoming mail should be sent. SPF, DKIM and DMARC concern sender authentication and related receiver policy; they are not a replacement for the recipient's MX configuration. Adding sender-authentication records to a recipient domain does not force an unrelated website to accept that address.
Identify the stage
- Signup form rejects the address: this may be the website's domain policy, before any email is sent.
- Sender reports a bounce: read the delivery status for the actual rejected stage and reason.
- Sender says queued: it may still be waiting to attempt or retry delivery.
- Receiver accepted the message: storage, filtering or display can still affect when it becomes visible.
Collect a useful report
Provide the complete recipient address, approximate sending time and timezone, sender identity and any bounce text with private information removed. A screenshot of an empty inbox alone does not show whether the sender attempted delivery.
Respect service restrictions
Some services do not allow disposable addresses. Another domain is not a guaranteed workaround, and a domain that works today may be treated differently later. Use an accepted, maintained mailbox for accounts that require dependable recovery.
For background, see Cloudflare's DNS record reference and Google's email sender guidelines.