WAMUG rejects sigantures ?

[Psychological Health Care]

I recently sent an email to the WAMUG list with the usual signature 
(using Mail in OS 10.3.2) and it was returned with the following 
introductory paragraph:

Failed to deliver to '<wamug@wamug.org.au>'
LIST module(list wamug) reports:
 Your message cannot be posted.
 It has the content-type: multipart/alternative,
 and this list accepts text only
Is this normal?  Do I really have to turn off my signature in 'Mail' 
when sending emails to the list?...  Is this the same for everybody?

Phil