Site not receiving e-mail

My organisation does not have a full-time

Internet connection.A demand-dial router

connects the intranet to the company's ISP

The ISP gives my site a user account and

static IP address. The ISP agrees to queue

EXCH-01 e-mail on its SMTP server so that my

site can retrieve the queued e-mail.

I discover that my site is not receiving

e-mail from the internet. i need to ensure

that EXCH-01 can retrieve e-mail that is stored

at the ISP?

What should I do?

A. Configure an SMTP connector that sends the

HELO command

B. Configure an SMTP connector to forward all

outbound messages to the ISP's SMTP server and

issue an ETRN command

C. Configure your SMTP virtual server to use the

ISP's SMTP server as a smart host

D.Configure your SMTP virtual server to use the

same DNS server that is used by the ISP's SMTP

server as an external DNS server

I think b. this shall ensure direct connectivity