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SMTP Transaction Time

Posted: Wed Apr 18, 2012 5:28 pm
by spaceout
When I run the SMTP diagnostics tool on http://www.mxtoolbox.com against my mail server, I always get about a 12 to 15 second transaction time and they report this as being "not good". I assume this is caused by one of the various mail filters running. Is this something that should be of great concern? Does anyone have any advice as to what I could look for to improve this time?

I'm running...
- Plesk 9.5.4
- qmail
- spamassassin
- qmail-scanner
- spamdyke
- dcc
- razor-agents
- pyzor
- clamAV

My server usually runs with a really low load so I'm not sure where the hang up is at. The processing time in the qmail-scanner log usually shows about 15 to 20 seconds. Again, that seems a bit slow considering the light server load and what seems like should be an ample amount of ram (8GB).

zen.spamhaus.org is the only RBL I'm using and I know those can slow things down a little, but 12 seconds seems extreme. I've tried removing DCC as well and that doesn't seem to make any difference.

Any advice?

Re: SMTP Transaction Time

Posted: Wed Apr 18, 2012 6:08 pm
by Kalimari
Notice you use Spamdyke, is "greeting-delay-secs" set? An RBL lookup may affect the transaction time, but as no message is delivered by the MX Toolbox test, Spamassassin/DCC/etc stuff won't come into play. Try removing the zen RBL entry (if you've not done so already), setting greeting-delay-secs to 0 and test again.

Re: SMTP Transaction Time

Posted: Wed Apr 18, 2012 6:38 pm
by spaceout
Having zen.spamhaus.org set up in Spamdyke is definitely the culprit. If I disable that the transaction times goes down to under one second! At least I know what to tell my clients if they complain about that transaction time. I can't see disabling that RBL making any sense since that really does block a ton of spam.

Thanks for the help!

Re: SMTP Transaction Time

Posted: Wed Apr 18, 2012 6:48 pm
by Kalimari
Yeah, I'd definitely keep the zen RBL enabled, stops so much badness with very little cpu overhead, that's worth a few seconds of anyone's transaction time.

Re: SMTP Transaction Time

Posted: Thu Apr 19, 2012 10:02 am
by scott
Make sure you're using a locally caching DNS, that should help improve the rbl resolution speed