Thanks for posting this it’s a confusing scenario when the WHOIS shows a domain as “Already Registered” but it still appears available for registration. In my experience, this often happens because of registry synchronization delays or the domain being in a soft‑delete/refund grace period. Checking the domain’s status directly at the registry and contacting support for the registrar may help clarify what’s really going on. You can also refer to the official documentation for guidance on WHOIS servers and domain availability checks: https://docs.whmcs.com/domains/whois-servers/
letting services#add-a-whois-server-for-domain-availability-checks
Interesting thread I’ve faced similar issues with WHMCS where emails just wouldn’t send. One thing that helped: switch from PHP Mail to SMTP in Configuration → System Settings → Mail, and then check the activity logs for any errors at the exact time you tried sending.
Also make sure the “From” address is a valid account on your mail server if it doesn’t exist, many hosts just block the send. Good luck getting it sorted!