about the A and PTR for sending mail

[风河]

Hi,

I know maybe this is not related to DNS question, so please excuse me
if it's not that suitable.

I have two server IPs, the A records for them are:

mail.dnsbed.com.        300     IN      A       74.117.233.4
mail.dnsbed.com.        300     IN      A       74.117.232.204

The corresponding PTR records are:

4.233.117.74.in-addr.arpa. 36466 IN     PTR     dnsbed.com.
204.232.117.74.in-addr.arpa. 36453 IN   PTR     dnsbed.com.


But this setting can't make email sending successful.
The Postfix system says:

postfix/smtp[13775]: A65713180D9: to=<***@freenet.de>,
relay=mx.freenet.de[195.4.92.211]:25, delay=1.2,
delays=0.29/0.02/0.76/0.16, dsn=5.0.0, status=bounced (host
mx.freenet.de[195.4.92.211] said: 550 inconsistent or no DNS PTR
record for 74.117.233.4 (see RFC 1912 2.1) (in reply to RCPT TO
command))


Is there any RFC item said the A and PTR records must be consistent?
And why they must?

Thanks.