[SLL] mailhub relay without knowing accounts and throttling inbound by domain name and outbound with postfix?

[Jeremy C. Reed]

I provide a mailhub (which does greylisting and more).

I don't know the accounts for the target systems. I don't control the 
target final mail destinations.

Sometimes I get many queued emails that are "deferred (delivery 
temporarily suspended" because "Error: too many connections from" 
(my mailhub).

For example, one day I had over 662 different hosts send to unknown 
addresses (near 3000 emails total). It is over 828 different bogus 
recipient addresses. That is after dnsbl and greylisting and other spam 
checks. Not a huge amount but is critical since "too many connections 
from" is stopping legitimate traffic.

Not enough connections from the same remote host to really block on client 
connection rates (without limiting good traffic).

I am using postfix.

Any ideas on how to possibly throttle these emails?

Either by limiting how many target a specific domain in a set amount of 
time (as I can have a good idea what is acceptable)?

Limit how fast my postfix server relays?

I looked at .*_destination_.*_limit but doesn't seem to be what I want.

Also I don't see how anvil(8) can be used to throttle per a domain.

Also maybe parsing logs and maybe using qshape(1) can help detect these 
types of problems and work-around it. Any ideas about that?

By the way, it appears that some of the target mail servers aren't the 
final destinations either as they accept mail from unknown users, for 
example, I receive "status=sent (250 Ok: queued as 3CB08679499)" for 
obviously bogus recipients.

  Jeremy C. Reed