🚀 go-pugleaf

Hello Everybody!:)
 I'm working on a SMTP Client that send emails without the use of a local
SMTP server
 This works by extracting the domain part form the recipient email address,
then doing an MX lookup against a DNS server for that domain part, and
finally connecting directly to the SMTP server that the MX record point to,
to deliver the message.(Taken from the Indy Demo SMTPRelay of Allen O'Neill)
All works fine but when I insert email addresses in the CC or BCC fields
cause the program raises the following exception: " EIdProtocolReplyError
with message <username@otherdomain> recipient address rejected."
I used otherdomain cause I assumed I'm sending an email (in TO: field)  with
domain other than the ones in CC or BCC fields!
Shouldn't  the SMTP server (given to me by the DNS server) forward the
emails in CC and BCC fields to the proper servers??
Of course I can take only an email address from the CC  or BCC field at a
time then do an MX lookup against a DNS server for that domain part, and
finally connect directly to the SMTP server that the MX record point to, to
deliver the message, but I need the email to arrive with the correct header,
that is with the correct email addresses in the CC or BCC fields!!
Any workaround??
Thank You very much in advance!!
Stefano B.