Both A and B people has mail client to mail client (i'm sorry to specify but
outlook to lookout) interaction happily.

1) mails from A company unix server 'uuu' (solaris) are being received by
A company people onto their outllook mail client. So A company people are happy.

2) mails from A company unix server 'uuu' (solaris) are not being received by B company people onto their outlook mail client. So B company people are
worried ???

Why A's unix server not sending mails to B's mail clients ???

Please note : solaris unix server is sending mails out through mailx client.