-return string_append(g, 4, US";\\n\\tspf=", spf_result,
- US" smtp.mailfrom=", expand_string(US"$sender_address_domain"));
+g = string_append(g, 2, US";\n\tspf=", spf_result);
+if (spf_result_guessed)
+ g = string_cat(g, US" (best guess record for domain)");
+
+s = expand_string(US"$sender_address_domain");
+return s && *s
+ ? string_append(g, 2, US" smtp.mailfrom=", s)
+ : string_cat(g, US" smtp.mailfrom=<>");