Conversation with gmail smtp timed out while receiving the initial server greeting

[h1j4ck3r]

Hello there!

Some weeks ago I've started to build a FreeBSD 6.2 mail server with
Postfix, Dovecot etc. Everything works fine except one thing - every
message I try to send to gmail subscriber is not accepted by the
google smtp servers. The error message I get in my mainlog is:

"conversation with gmail-smtp-in.l.google.com[72.14.221.114] timed out
while receiving the initial server greeting"

or similar to this.

Can someone give me advice or something why this happens? At this
moment this problem appears only with gmail.
Could this be some reverse DNS issue?
Thanks in advance!