Sendmail (slow) versus Postfix (fast)?

[retrix]

I'm hoping someone can help me out here. I have two servers running FreeBSD (4.x) with Sendmail, both using bl.spamcop.net to reject spam. About a month ago or so, we noticed that connecting to our SMTP server got slower and slower. It now takes almost a minute before the 220 connected message. On the same network, we have another server which uses Postfix, and the 220 message comes up almost instantaneously. Disabling the use of bl.spamcop.net with the Sendmail servers eliminates the delay, so it is definitely something to do with this.

From the command line, I did a manual lookup (ie. dig a 4.3.2.1.bl.spamcop.net), and a response comes back right away (< 100 ms). So, I'm hoping someone else has experienced this insane delay with sendmail, and has some sort of solution. We are planning to completely switch to Postfix, but until then, I'd like to resolve this. I've had to disable spamcop on our main mailserver, using several other blacklists instead because the delay is just too long for our customers.

Any ideas/help would be greatly appreciated.

Thanks,

Patrick

[sommerfeld]

Use a system call tracer (ktrace/kdump on *BSD?) to narrow down what's happening around the lag time.

Use tcpdump to see what dns queries it's generating and when..

Collect both traces with absolute timestamps, correlate the two traces, and see if anything pops out as

unusual..

[Wazoo]

I'm thinking you'll have a better shot at getting a response elsewhere ... for instance, the newsgoups at news://news.spamcop.net/spamcop ... there are other admins there that may be able to jump in (most choose not to deal with this web-based thing) .. will just note that this is the first time I've seen this issue brought up. Have you been to Sendmail.net/org/com (depends on which version you're using)? Do you/your ISP carry the sndmail newsgroup?