MUAs we use

[Ralf Mardorf]

PS:

Even if you would include X-Mailer and would get additional results
such as "Apple Mail", "Claws" ... you need to ensure that all mails are
available, that came through the list and only those. You need to
provide the information about the uniqueness, how many subscribers use
more than just one MUA etc., pp. In the end it would result in an
accurate statistic, that anyway would be more or less meaningless.