SMTP no-such-user issues

Steve Bertrand steve at
Tue Jun 17 16:38:22 UTC 2008

Steve Bertrand wrote:
> Shane Short wrote:
>> are you using vpopmail with your qmail install? (I can't seem to load 
>> your errors again, I recall they were chkuser failures)
> Yes, vpopmail against MySQL.
>> I've had this problem before when I've run out of MySQL connections 
>> and vchkuser was then failing.
> Thanks for the feedback, but this is not the case.
> The problem has been identified to be extraordinarily site specific. I'm 
> attempting to follow the recommendations of members that mailed me off 
> list one at a time, and am proceeding with testing.
> It would be of great value if other mail admins who are running Qmail 
> that have a few minutes could contact me off list in order to compare 
> some quick test results/config setups.

Well, in order to draw a conclusion (not yet tested), someone mentioned 
off-list to look at the extended function PIPELINING.

After reviewing this possibility, it directly fits the bill in regards 
to the issues I have been experiencing. I will disable it just as a pure 
test, however, after scouring the web to weigh the benefits to 
drawbacks, I've found a pretty general consensus that disabling 
pipelining because of a single poorly-implemented client will 
effectively erase any performance enhancement that well-behaved clients 
can achieve with it.

If this does turn out to be the problem, then the users, whom are out of 
my control, of the single site who are witnessing this problem that 
appears to originate from my end can deal with sorting through the 
apparently 'faulty' list of addresses they receive in the bounce.

Does this theory sound reasonable, and is keeping pipelining in place a 
recommended option?


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