Hi @margarit0,
WP-SpamShield is 100% compatible with PHP 7+, including PHP 7.1. It will always be compatible with the latest and greatest stable PHP version.
The issue you’re talking about is a common one among contact form plugins. It’s not specific to any particular contact form plugin, and is not related to the plugin code or PHP version.
The issue has to do with email being sent from the server, instead of using SMTP on a real email account. Sending mail through a web server (instead of SMTP) is notoriously unreliable (unless you are very experienced with email configuration). We have an FAQ about it with more info:
Please see the sticky post at the top of the forum — PLEASE READ BEFORE POSTING — Updated June 2017, and follow the links there to our support documentation and to our official support page. (These links are also in the plugin’s settings page.)
Please note that we don’t provide support here at the forums, but we do provide excellent support through our site, which is better equipped to help our plugin users.
Please direct all support requests to the plugin’s official support venue, the WP-SpamShield Technical Support page.
–- Steven