Problem with Dns resolve lookup
I am administering a server that hosts a mail server(sendmail, dovecot,spamassassin,clamav) and webserver (httpd, squid). The last a couple of days I have problem with e-mail, when another mail server requests (for example a bank ) reverse lookup in order to accept my e-mails. It seems like there is no in-address-arpa for my domain. The current setup,doesn't actually need a full blown DNS Server because my ISP provides DNS resolution for me.
When I contacted my ISP to add a PTR record their reply was that the problem is with the ISP of the remote site(bank) and not with them.
But I have e-mails that are for other recipients and they also stay queued because of the same problem.In the past I never had a problem and I haven't changed anything from my setup
By the way I have upgrated my Centos to CentOS 5.2.
I still think the problem is with my ISP.
Any suggestions on whta can I look for?