ISO 8601 is meant as the standard way to provide an unambiguous and well-defined method of representing dates and times. And the fact that it is widely used in e-mails doesn't make it e-mail specific.

Incorporating function parsedate_to_datetime to email.util is acceptable. But the fact that standard python datetime library doesn't have means to parse ISO-approved time format seems strange to me.

Once again: ISO 8601 is not a e-mail specific format. So I do not see a reason why parsing it is possible only via email.

Using different time-parsing functions in different libraries seems like a bad design to me.