Delayed Mail

[Matt <mhoppes@gmail.com>]

Hi List,
I have 9 mail servers, using ldap as the backend authentication system.  They all deliver to a NAS unit.     Out of the 6 system, 3 are old machines (500-800mhz), 2 are dual core xeons, and 1 is a P3 2.8Ghz.   All have 
1.5GB of memory, with the P3 and xeons having 2GB of memory.

Here's my question... what would cause a high level of unprocessed messages?    On the 3 old machines I never see this problem (odd!), yet the P3 will often end up grinding and slowing down, maxing out its connections, and then finally start getting unprocessed messages.   At that point, I firewall off port 25 and let us deliver.

I have checked and I am running the same version of SPAMD, CLAMAV on all the systems.    My guess is that a spam run is triggering spamd to do some extensive scanning on the mail.... but then why would the older machines not have the same issue?  Even when/if they get totally bogged down, they have never ended up with unprocessed messages.


TO BE RESOLVED:
1 - What might be causing these unprocessed messages?  Is it a bottle neck?
2 - How do others adjust their concurrencyincomming?   It seems that even 40msg concurrent can swamp the P3 2.8GHz
, depending on the incoming mail... yet it will be fine for weeks... likewise, I've seen the Xeons go fine with a max of 254, but that can easily kill them if a huge spam run comes in.

Thoughts?