Sendmail 'Too many connections' problem

[Steven W. Orr]

I run sendmail-8.13.8 at home to host my domain. Some domains will not 
accept mail from me because my address is from a dynamic address pool so I 
solved that problem by placing all of those domains in my mailertable and 
now route those messages through my ISP(RCN). Recently I have noticed that 
some of the mail is hanging for a while with 400 series messages saying 
'Too many connections'. I checked with RCN and after many wasted hours on 
hold I found out that I need to limit the maximum number of connections to 
their SMTP server to 4. Four shall be the counting. Five is too many and 
six is right out!

Can someone please tell me what the incantation is to limit the number of
simultaneous connections to a particular server? I'm not looking to limit 
incoming conncetions. I'm not looking to limit the rate of incoming or 
outgoing connections. I just want to set the max nr of connections from me 
to RCN to no more than four.

TIA.