There are websites, blogs etc in Afrikaans, where people also post reactions. As Afrikaans seems to be available in practically every domain to some extent (in specific regions), there is nothing that indicates that Afrikaans is not used for E-mails and text messaging. To suggest rather the opposite, for example, there are websites in Afrikaans, which invite people in Afrikaans to contact them or react to them via E-mail or text messaging.