Completely different to standards-compliance, yes. However it is exactly the same thing as GMail's alphanumeric only rule. To reiterate - the mailbox names th

Completely different to standards-compliance, yes. However it is exactly the same thing as GMail's alphanumeric only rule. To reiterate - the mailbox names that a email provider will provide are subject to the naming conventions defined by that provider. Whether the convention is firstname.lastname; 5-7 characters only; alphabetic only; or 13375p34k transcriptions of characters from Lord of the Rings. None of that has anything to do with whether they are standards-compliant. The test is whether they will send email to any RFC-compliant email address regardless of whether it conforms to their own mailbox naming convention. Gmail does.