In this article, we discuss the most common causes and solutions to the '421 4.7.0 An Internal Server Error has occurred. SPF records for example.com could not be verified’ error message. Simply put, this message means that the SPF check for your domain has not been successful:
When you send an email, the receiving party automatically checks your SPF record. In an SPF record, you determine which servers can send email on behalf of your domain. The 421 4.7.0 error message means that the recipient has received the email from a server that does not match with what is in your SPF record.
We mainly come across the following three causes of this problem:
- WordPress web forms which mail via SMTP
- An incorrect email address sends the email
- An invalid or non-existent SPF record
WordPress web forms that do not mail via SMTP
Suppose you host a WordPress website with us on a web hosting subscription, or a VPS combined with our VPS mail service. In that case, you use our mail servers to send mail on behalf of your domain. Your DNS records can look like this:
Here, the SPF record has the value: v=spf1 include:_spf.transip.email ~all
This record ensures that our mail servers can send mail on behalf of your domain. However, many web forms use the PHP mail () function, which ensures that a web form sends mail from the server hosting the website (i.e. which is stated in the A record and / or AAAA record) and not via the mail server (which is stated in the SPF record).
In the DNS example above, you can see that the website is hosted on the IP address 95.170.78.147. In this example, the result of using a web form with the PHP mail () function would be the following message:
[95.170.78.147] said: 421 4.7.0 An Internal Server Error has occurred. SPF records for example.com could not be verified. Please try again later. Please see https://www.transip.eu/question/110000767 for more information.
Here, you can see the IP address from the A-record (see the previous screenshot). This is a clear sign that mail is being sent from the server hosting the website and not from the mail servers in the SPF record (in this example, these are our mail servers).
Do you see a subdomain in this error message, for example, server.example.com? Then, take a look at the 'An incorrect email address' section.
Solving the problem
In this case, there are two options to solve the problem:
The easiest is to add the IP address which sends the emails to your SPF record. There are two ways to do this:
-
Option 1: Does the IP address from the error message match an IPv4 or IPv6 address that is in your root A record or AAAA record, as in the example below?
In that case, you can simply authorize these IP addresses in your SPF record with the addition a, i.e.:
v=spf1 a include:_spf.transip.email ~all
The a addition authorizes all A and AAAA records from the DNS records for your domain.
-
Option 2: In other cases, you can add the specific IPv4 or IPv6 address to your SPF record:
v=spf1 ip4:95.170.78.147 include:_spf.transip.email ~all
Replace 95.170.78.147 with the actual IPv4 address from the error message. For an IPv6 address, use:
v=spf1 ip6:2a01:7c8:eb::95:170:78:147 include:_spf.transip.email ~all
Replace 2a01:7c8:eb::95:170:78:147 by the actual IPv6 address from the error message.
- The addition include:_spf.transip.email is only required if you use our mail servers. This applies to our web hosting packages and VPSs which use the VPS mail service.
- SPF records allow for more configuration options than those covered in this article. More options can be found in our SPF article.
Many web forms do not offer SMTP support by default. In that case, you can install an SMTP plugin on your website, such as https://wordpress.org/plugins/wp-mail-smtp/
To be able to use this plugin to mail via a contact form from your website, you will need to set the following information:
SMTP Authentication: Yes
SMTP Security: SSL
Port: 465
Username: the email address from where you want to mail
Password: the password of this email address
Host: smtp.transip.email
An incorrect email address
In this case, the email is sent from another domain (e.g. on behalf of @random.com) than the desired domain (e.g. @example.com), or the mail is sent from a subdomain (e.g. info@server.example. com instead of info@example.com). You will then see an error message such as:
[95.170.78.147] said: 421 4.7.0 An Internal Server Error has occurred. SPF records for server.example.com could not be verified. Please try again later. Please see https://www.transip.eu/question/110000767 for more information.
In this example, server.example.com is the piece with which you can see that a wrong email address is being used.
The cause can be very different, and it is therefore best to check how the email is sent and which email address has been set for it. Two examples of this which we encounter more often are:
- A WordPress form which emails on behalf of the hostname, in which case we recommend an SMTP plugin.
- A VPS with a control panel such as DirectAdmin automatically sends emails (e.g. for a security system) on behalf of an administrator email address, or the subdomain set as the hostname.
In this case, it is advisable to check where the email address has been set and to adjust it.
If in doubt, you can always ask our support department for advice. In that case, please send the exact bounce notification.
An invalid or non-existent SPF record
The 420 4.7.0. notification can also appear when no SPF record is set, a wrong SPF record is set, or you set up SPF records with us, but use nameservers from another party. The best way to rule out this cause is to check your DNS records and nameservers. Here are three examples of invalid / non-existent SPF records:
No SPF records
Below, you can see a screenshot with our standard DNS settings for domains without a web hosting subscription as an example.
You do not see an SPF record here. (An SPF record can be recognized by the type 'TXT' and that the value starts with v=spf). In this example, the DNS records do not even point to the server(s) hosting your website and / or email at all. You solve the problem in this example by setting the DNS records for your domain.
Other name servers
Suppose, you do not see our name servers in your control panel, as in the example below, then, check the SPF records with the party whose nameservers you are using (Wix in this example). How that works depends on the party in question. It is best to contact them in this case.
Incorrect SPF record
In other cases, where you have set up an SPF record, but it may not be complete, follow the previous 'Customize your SPF record' instruction.
This concludes our article on the 421 4.7.1 email error. Should you have any questions left regarding this article, do not hesitate to contact our support department. You can reach them via the ‘Contact Us’ button at the bottom of this page.