Sendmail - Connection rate limit exceeded.

[nx13441a <nx13441a@net.vodafone.pt>]

Hi,

I'm using sendmail 8.13.3-9
I'm getting:
Mar 16 09:41:16 xxxxxxxx sm-mta[16412]: ruleset=check_relay, arg1=relay6.xxx.xxxx.xx, arg2=21x.5x.xxx.xx, relay=relay6.xxx.xx.xx [21x.xx.xxx.xx], reject=421 4.3.2 Connection rate limit exceeded.

My sendmail.mc:

define(`confCONNECTION_RATE_WINDOW_SIZE', `45m')dnl


Why?

thanks in advance.