WordPress 4.9.2更新后Contact Form 7提交失败，求解决方案

Hey there, sorry to hear you're dealing with this frustrating issue across all your Contact Form 7 (CF7) sites after WordPress 4.9.2's auto-update. Since you've narrowed it down to a WP version-specific problem, here are the most reliable fixes that worked for other developers in the same boat:

1. Roll Back WordPress to 4.9.1 (Quick Emergency Fix) #

Since you confirmed the problem is isolated to WP 4.9.2, rolling back to the previous stable version will get your forms working again immediately:

• First, back up your site files and database—never skip this step!
• Use FTP to replace the wp-includes and wp-admin folders with the corresponding folders from a WordPress 4.9.1 installation package.
• If you can still access your WP admin, use the WP Rollback plugin to safely revert the core version without FTP.

2. Update Contact Form 7 to the Latest Compatible Version #

Right after WP 4.9.2 launched, the CF7 team released a compatibility patch. If you're running an older CF7 version, updating it should resolve the conflict:

• Go to Plugins > Installed Plugins in your WP admin, find Contact Form 7, and click "Update Now".
• If the admin update fails, manually download the latest CF7 version, then use FTP to overwrite the wp-content/plugins/contact-form-7 folder (backup the original folder first).

3. Fix PHPMailer Compatibility Issues #

WP 4.9.2 updated its PHPMailer library, which clashed with CF7's default mail setup for many sites. Try these tweaks:

• In your CF7 form settings, go to the Mail tab. Under "Mail Settings", switch the "Send mail via" option from the default mail() function to SMTP (if you have an SMTP server configured—this is more reliable anyway).
• Alternatively, replace WP 4.9.2's PHPMailer files with the version from WP 4.9.1:
  1. Extract wp-includes/class-phpmailer.php and wp-includes/class-smtp.php from a WP 4.9.1 installation.
  2. Upload these files via FTP to overwrite the ones in your WP 4.9.2 site's wp-includes folder.

4. Rule Out Theme/Plugin Conflicts (Fallback Check) #

Even though you've pinpointed the WP version issue, it's worth a quick check to eliminate other variables:

• Switch your site to a default WordPress theme (like Twenty Seventeen) and test form submission.
• Disable all plugins except Contact Form 7, test the form, then re-enable plugins one by one to spot any conflicts.

Note: WordPress later acknowledged the mail-related compatibility bugs in 4.9.2 and fixed them in version 4.9.3 and above. If possible, updating your WordPress core to 4.9.3 or a newer stable version is the most permanent solution.

内容的提问来源于stack exchange，提问作者Johan Carlsson