Use SPF v=spf1 mx -all for Email DNS upserts.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/mail-dns/mail-dns.ts

@@ -1,7 +1,7 @@
 export const MAIL_IPV4 = '185.214.101.41';
 export const MAIL_HOSTNAME = 'mail.meshkee.com';
 export const MAIL_MX_PRIORITY = 10;
-export const MAIL_SPF = `v=spf1 ip4:${MAIL_IPV4} -all`;
+export const MAIL_SPF = 'v=spf1 mx -all';
 /** Old provider selector (dkim._domainkey.example.com) — removed on mail DNS update. */
 export const LEGACY_DKIM_NAME = 'dkim._domainkey';
 export const DMARC_NAME = '_dmarc';