About rDNS

Hi all,

Sorry for my poor English.

I do not know much about DNS and I really need the advice of experts

I've a web server with a smtp serveur (Lumisoft) used just to send mailings
from different web sites located on the same machine. This smtp server is
innaccessible from outside, juste localhost is able to connect and send
mail. No account configured.No MX record is pointing to our IP.
Mails are sent using DNS (not with a relay).Sender's email address is
variable (for site www.siteA.com sender adresse is and for
site www.siteB.com sender is ).
We do not host the DNS and we do not have the ability to configure them
ourselves. We just asked to create a type A record www that points to our IP
address.

The problem: mails sent are considered as spam because we have no reverse
DNS. Can I ask to an ISP to create a reverse DNS to our server web IP
address?
Is it possible for them to create a rDNS like [our ip address].in-addr.arpa
corresponding to mail.siteA.com while we have no corresponding MX record
that points to our IP?
And finally, is it possible to have multiple rDNS that point to a single IP
address?

Thank you for your patience.

JLE