DATA line too long error when sending HTML message using Indy SMTP

I keep on getting the following error message bounced back from a
particular service provider when I send a html message...

550 DATA line too long (Max 1024)

This is only happening with one particular ISP, the message seems to
be handled fine by everyone else.  The message is in html and includes
about 4 images, I've double checked the length of each line in the
message and all of them are well under 1000 bytes.  I was wondering if
anyone has any ideas as to how I can fix this problem, I am assuming
that this has something to do with the way the attachments are encoded
within Indy, as I can't see how it can be the message body part of the
text.

I am using Delphi 5 with Indy 8.00.23