Not having an email address is not a special case when it comes to IM service identifiers. Many of the most popular services, such as Skype and AIM, use other types of identifiers.
As mailto:// is only to be used for valid email addresses, I'd say it's insufficient for our needs.
Not having an email address is not a special case when it comes to IM service identifiers. Many of the most popular services, such as Skype and AIM, use other types of identifiers.
As mailto:// is only to be used for valid email addresses, I'd say it's insufficient for our needs.