Why is 1@1.1 valid?

[KirbyDE]

The address 1@1.1 is reported as valid, but doesn't seem to be accepted by SMTP servers.

Is this a bug?

[egulias]

Hi Kirby.
The RFC's that specify email sintax are not necesarily implemented in full by all versions of all STMP servers.
If you are using v2, the domain validation was very loose in that it followed email's RFC rather than domain RFC 1035.
v3 is closer to RFC 1035 so it might come out as invalid, for instance.
But, even if by "formal" definition a domain or an email address is valid, is does not mean it will be accepted 100% of the times by all SMTP servers.

[Zenexer]

RFC 1035 permits 1.1 as a valid name.

[KirbyDE]

Thanks for the reply.

I've tested v3 and it seems like 1@1.1 is reported as valid.

Could this be changed?

As far as I understand RFC 3696 an email ending in an all numeric TLD can't be valid:

There is an additional rule that essentially requires that top-level domain names not be all-numeric

[Zenexer]

That additional rule is enforced by ICANN and only applies to public zones that they administer. You can most certainly have a zone within your own DNS system that is all-numeric.

There's nothing stopping an organization's internal email infrastructure from using and accepting 1@1.1; it just won't be usable on the public internet via traditional, ICANN-administered DNS.

[Zenexer]

Note that if you want to forbid 1.1, you can probably use DNSCheckValidation instead of or in addition to RFCValidation--although if your DNS resolver is capable of resolving zones other than those administered by ICANN, there's still a possibility it will be considered valid and that email can be delivered.