Contact Form 7 4.4 has introduced Configuration Validator, which validates contact form configurations to detect errors leading to mail delivery failure or other troubles. This article explains the expected input for each setting field, common mistakes, and how you can resolve those errors.
See also: FAQ about Configuration Validator
Mail To Field
The To field specifies the email address of the recipient who receives the mail.
You can use mail-tags in this field. If you use mail-tags, ensure that the mail-tags are replaced with email addresses. Otherwise, it causes a syntax error.
You can also set multiple addresses here. In such cases, use a comma to separate addresses.
Mail From Field
The From field specifies the email address of the sender.
You can also use another format consisting of a name and an email address surrounded by “<" and ">“.
John Smith <email@example.com>
You can use mail-tags in this field. If you use mail-tags, ensure that the field will be in the correct format after the mail-tags are replaced with user inputs. Otherwise, it causes a syntax error.
The email address used in this field should be an address belonging to the same domain as the site. Otherwise, it can increase the likelihood of being treated as spam.
Mail Subject Field
The Subject field specifies the subject of the message. It’s basically a free format, but it can’t contain markups like HTML tags.
The subject is not allowed to be blank. If you use mail-tags here, ensure that it’s not blank even after the mail-tags are replaced with user inputs.
Mail Additional Headers Field
You can set additional mail headers in the Additional Headers field. Content of this field (if it’s specified) must follow the syntax specified in the standard specification (RFC 5322). Otherwise, it will cause a syntax error.
Additional mail headers commonly used are: Cc, Bcc, and Reply-To.
Cc: firstname.lastname@example.org Reply-To: email@example.com
Mail Message Body Field
The Message Body field is the message body of the mail. It is free format, but if it’s blank, the mail host may refuse to deliver the mail. If you use mail-tags here, ensure that it’s not blank even after the mail-tags are replaced with user inputs.
In the Messages tab in the contact form editor screen, you can edit messages that Contact Form 7 displays in different situations. You can only use plain text in the messages; do not use HTML tags and entities.
See also: HTML is Not Allowed in Messages
The active support forum volunteer, buzztone, explained in his blog post why this configuration validator was important, and how to resolve errors in further detail. I recommend you read it if you are still uncertain after reading this article.