GW 5.5 and multipart/alternative emails

[chrism]

Hi,

Could anyone possibly tell me if GW5.5 can compose and send emails
that I think use the multipart/alternative MIME type.

I am wanting to send an email that will appear as HTML to those who
have it enabled and as text to those who don't.

Obviously the client software will vary as it will be mailed to
supporters of our charity, so if there will be problems receiving the
email in particular versions that I could be made aware of, I would
like to know.

I haven't been able to find much information, generally, on the
subject so any info that would make it easier for me to decide if I
should be doing it through GW in the first place would also be
appreciated.