email sent in parts. notes client cannot receive it.

I am using the qtmmsendmail api to send an email msg with a pdf attachment.
The PDF file is a little over 100k in size and apparently the as400 mail
client is sending the message as two messages.

I say this, because when my outlook 2000 client receives the message a brief
message is displayed saying that the two message parts are being combined.
Once that is done, the message shows as a single message in outlook and the
attachment are readable. As the pc programmers say, +1 for outlook.

But, when I send the same message to a domino/notes email address, the
recipient receives an "undeliverable mail" message.
   ERROR IN BATCH SMTP COMMAND SEQUENCE.
   Ending sequence <CRLF>.<CRLF>
   550 Partial e-mail rejected

Any idea where the problem lies?  Can the threshold at which the as400
splits an email message into parts be increased?

thanks,

Steve Richter