A developer of a TCP/IP network contributed the following tip.
MacWorkStation does support MARK parity, even though it is used on some
mainframes. To work around this, try defining settings as follows:
Mark parity, 7 data bits, 1 stop bit
as:
No parity, 7 data bits, 2 stop bits
This kludge seems to be working, but MacWorkStation should support all
parity settings, including EVEN, ODD, NONE, SPACE, and MARK. Note that NONE
can mean no parity bit (NONE) or a zero bit (SPACE), depending on the
vendor.