DNS Zone file configuration

[Commdude]

I've had several problems which I'm sure are related to my DNS configuration. Here's my record for my main domain:

"A" RECORD: @ 71.39.7.66
www 71.39.7.66
netsrvr1 71.39.7.66
smtp 71.39.7.66
CNAMES (Aliases): None
MX (Mail Exchangers) : 0 @ netsrvr1.bitterbrushnet.com
TEXT: @ v=spf1 a ptr mx:smtp.bitterbrushnet.com -all

My reverse DNS record is configured as:
71.39.7.66 >>> bitterbrushnet.com My ISP only allows one entry per IP address. Is this normal, or is it just them?

I had problems (mail test failure) when I used smtp.bitterbrushnet.com in the MX record. When I changed it to netsrvr1 (my real hostname as configured during initial installation) I was able to receive mail. So, (1) what is the optimum zone file configuration, and (2) how does this apply to virtual hosts? Do their MX records read "smtp.virtualhost.com"?