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Error “Could not instantiate mail function” When Sending Emails

If you are getting the error “Could not instantiate mail function” when trying to use the Send Email action, your server may be misconfigured for sending emails.

This is not a WS Form bug.

By default, WS Form sends emails to:

  • #blog_admin_email – The Administration Email Address found in WordPress Settings > General
  • #blog_name – The Site Title found in WordPress Settings > General

You can change these settings.

This article describes possible solutions to this problem:

Using a Local Web Server (e.g. WAMP)

Local web servers typically do not have a mail server running. This will prevent emails from being sent.

You should use an external SMTP server in conjunction with an SMTP plugin.

An Email Address is Invalid

Ensure your Send Email settings are correct and that your From and To email addresses are valid.

Sending emails From and To the same email address may, on occasion, cause issues.

Learn More

Your SMTP Plugin Cannot Accept Display Names

WS Form supports display names for email addresses (per RFC 2822). The WordPress wp_mail function also supports this format.

An example of this email address format is: joe.bloggs@emailtmp.com <Joe Bloggs>

We have found that some SMTP plugins have a bug that causes email addresses in this format to break the sending of emails.

Known plugins with this issue:

  • FluentSMTP
  • SendInBlue (Fixed in version 3.1.38)

We would suggest trying to remove the Display Name setting and then try to send the email again to confirm if this is the case with your SMTP plugin.

WS Form - Send Email - Clear Display Name

Invalid Subject Line

Avoid punctuation and special characters in your email subject line. Some mail servers will reject emails that contain certain characters. Keeping your subject line to alpha-numeric characters will increase your chance of deliverability.

Also ensure your subject line is not too long. We recommend keeping subject lines between 10 and 60 characters long.

Exceeding Quotas

Some SMTP providers impose quotas on how many emails you can send. If that quota is exceeded you will no longer be able to send emails. Login to your SMTP provider account to check your send count, quotas and frequency caps.

More Information