Simon Prosser

Thank you, the fix looks good!

Im not sure I understand your fix.

In a previous support thread here it was said that you tried to add angle brackes before and had to remove them as it broke support for something else, so my PR added a filter to allow uses to add the brackets if the desired and leave the default as it was, I gave you a PR for that.

I downloaded the “beta” version and it looks like you are now adding the angle brackets anyway now so breaking backwards compatibility and the filter now does essentially nothing.

    private function apply_default_headers( $message ) {
        /**
         * Filter the Message-ID addr-spec (unbracketed id@domain) before the RFC 5322 header is built.
         *
         * @since 3.9.2
         *
         * @param string $addr_spec Message-ID without angle brackets.
         */
        $addr_spec = apply_filters( 'post_smtp_message_id', $this->createMessageId() );
        $addr_spec = trim( (string) $addr_spec );
        $len       = strlen( $addr_spec );
        if ( $len >= 2 && '<' === $addr_spec[0] && '>' === substr( $addr_spec, -1 ) ) {
            $addr_spec = substr( $addr_spec, 1, -1 );
        }
        $headers[] = 'Message-ID: <' . $addr_spec . '>';
        $message->addHeaders( $headers );
    }