BT reverse ptr records

[C]

Hi
hope this is the best group to post this in

i have just moved over our office to BT from easynet

with easynet we had our dns setup so we could run a mail server from the office.   the domain had a sub domain 'mail.mydom.com' and easynet setup a reverse record for this as well

since moving to BT we have the same setup internally, however BT will not change their reverse dns ptr/in-addr records to match our domain and i am worried that this will lead to mail being returned because the reverse lookup does not match the domain it comes from 

is this true and if so how can i get round this

thanks 
Craig

ps please reply to the group thats not my real email