On 8/4/2012 9:19 AM, Wietse Venema wrote: > Stan Hoeppner: >> Would someone kindly point me to the docs that describe the behavior of >> smtpd socket open time in relation to clients that do connection caching? > > http://www.postfix.org/postconf.5.html#smtpd_timeout > > It's stress-dependent.
Thanks Wietse, will be reading shortly. >> I've been assisting in a troubleshooting effort. A sendmail/mailman >> based list server is opening more than 4 concurrent connections to my MX >> even when it has less than a half dozen messages to deliver, which >> suggests connection caching on their end is not working properly. > > Does your box have multiple IP addresses? When Sendmail gets a 4XX > RCPT TO reply, it will try to connect to an alternate address WHILE > KEEPING THE 4XX-ed CONNECTION OPEN. I see this all the time with > my postscreen setup. No, single IP, and a single MX for the domain. > postscreen listens on multiple IP addresses, and uses > postscreen_whitelist_interfaces to block clients that connect to > the backup address only. I never implemented postscreen as my volume is too low to really need it. I think the main problem with this list server is that they had set # open connection cache size O ConnectionCacheSize=5 # open connection cache timeout O ConnectionCacheTimeout=5m The default for the first is 1 and the docs say never go over 4. The default for the 2nd is 5 mins. They've since, at my prodding, changed the cache size, to 2. I recommended going back to the default which is 1. AFAIK anvil hasn't tripped since these last changes but it's only been a couple of days and list traffic has been mild. Dropping from 5 to 2 should reduce memory pressure on their host, and I'd think going to 1 would help even more. But that has nothing to do with postfix so sorry for veering a little OT. Anyway, I was just wanting to understand the postfix smtpd behavior to better understand the interaction between the hosts. Thanks again Wietse. -- Stan
