Adjust max domain length check from 63 to 255

resources/spf/basic.yml

@@ -1,17 +1,17 @@
-# If the <domain> is malformed (e.g., label longer than 63 characters,
+# If the <domain> is malformed (e.g., total length longer than 255 characters,
 # zero-length label not at the end, etc.) or is not a multi-label
 # domain name, or if the DNS lookup returns "Name Error" (RCODE 3, also
 # known as "NXDOMAIN" [RFC2308]), check_host() immediately returns the
 # result "none".
 
 name: Malformed Domains
 records:
-  spf: extremely.ridiculously.long.domain.name.that.should.fail.immediately.com v=spf1 +all
+  spf: this.domain.name.is.extremely.long.because.we.want.to.explicitly.show.that.the.maximum.length.of.a.domain.name.is.255.characters.so.this.one.will.definitely.fail.immediately.due.to.its.excessive.length.and.ridiculously.large.number.of.characters.which.makes.it.invalid.com v=spf1 +all
   spf: nolabels v=spf1 +all
   spf: none.test.org v=something-else not=spf for=sure
 tests:
-  - domain: extremely.ridiculously.long.domain.name.that.should.fail.immediately.com
-    sender: sender@extremely.ridiculously.long.domain.name.that.should.fail.immediately.com
+  - domain: this.domain.name.is.extremely.long.because.we.want.to.explicitly.show.that.the.maximum.length.of.a.domain.name.is.255.characters.so.this.one.will.definitely.fail.immediately.due.to.its.excessive.length.and.ridiculously.large.number.of.characters.which.makes.it.invalid.com
+    sender: sender@this.domain.name.is.extremely.long.because.we.want.to.explicitly.show.that.the.maximum.length.of.a.domain.name.is.255.characters.so.this.one.will.definitely.fail.immediately.due.to.its.excessive.length.and.ridiculously.large.number.of.characters.which.makes.it.invalid.com
     ip: 172.168.0.1
     expect: none
   - domain: nolabels

src/spf/verify.rs

@@ -88,7 +88,7 @@ impl Resolver {
         sender: &str,
     ) -> SpfOutput {
         let output = SpfOutput::new(domain.to_string());
-        if domain.is_empty() || domain.len() > 63 || !domain.has_labels() {
+        if domain.is_empty() || domain.len() > 255 || !domain.has_labels() {
             return output.with_result(SpfResult::None);
         }
         let mut vars = Variables::new();