
This article is for resellers who run their own WHMCS. WHMCS is another company’s product: we neither sell nor resell licences, as explained in what WHMCS is. Menu names change from one WHMCS version to the next. The short answer: WHMCS sends invoices, reminders and ticket replies. When those messages do not arrive or land in spam, the cause is rarely WHMCS itself: it is the sending method (plain PHP mail instead of authenticated SMTP), a sender address that does not match the domain, or a domain without SPF, DKIM and DMARC. If messages never even leave the queue, check the cron job first in the most common WHMCS problems.
What goes wrong, and where it is fixed
| Symptom | Most likely cause |
| No customer receives anything | Sending is set to PHP and the receiving server refuses, or the SMTP details are wrong. The WHMCS e-mail log shows whether the message left. |
| It arrives, but in spam | The sender address belongs to a domain without SPF, DKIM and DMARC, or to a different domain from the one sending. See SPF, DKIM and DMARC. |
| Spam only at Gmail, or only at Outlook | The domain has no reputation yet, or the templates look like advertising. See a new domain sending e-mail. |
| The SMTP test hangs and ends with no answer | The wrong port for the encryption type, or the network will not let that port out. See ports 465 and 587. |
| Customers reply and the reply goes nowhere | The sender address is not a real mailbox, or it is not linked to the support department. |
Setting up sending through your own mailbox
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| Do not stay on plain PHP mail. Without authentication the receiving servers cannot tell the mail is yours, and invoices are the first to get lost. See mail() or SMTP. And if you point WHMCS at another provider’s SMTP and the connection never opens, ask us whether outbound connections to that server are allowed, rather than trying ports at random. |
| The e-mail log is the proof. WHMCS keeps a list of every message sent to each customer. If it is there and the customer says it never came, look in their spam; if it is not there, the problem is the sending or the cron job. |
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WHMCS mail still not arriving? Send us the sender address, one recipient that failed and the time it was sent. Open a support ticket |
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