This may or may not be a bug; it was suspicious so I am
reporting it.
I ran the script

#!/bin/sh -x
for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
19 ; do #

    /usr/sbin/sendmail support-issue@foo.com <<EOF
From: Will Partain <partain@foo.com>
To: support-issue@foo.com
Subject: [issue$i] [assignedto=partain]
EOF
done

to assign a whole bunch of issues.  It succeeded on all
but three
issues, where it apparently did nothing.  I ran those
separately later,
and they changed assignedto as expected.

"Silently not working" isn't really desirable (if
that's what it's doing).  It should be easy to test to
your satisfaction.  Keep up the good work!

Will

Logged In: YES 
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You got _no_ errors? Nothing to either of the partain@foo.com 
address or the roundup admin address?? 
 
What method are you using to handle email? 
 
The Roundup mail handler traps all errors in its code and reports them 
back to either the sender (if it's known) or the roundup admin (if 
there's no From address in the mail). 
 
Was it always three messages that didn't work? Always the last three? 
What's your local sendmail queue length - is there a chance that 
sendmail refuses to queue 20 messages (well, maybe less, depending 
on how quickly roundup processes the messages)? 
 

Logged In: YES 
user_id=10007

No, no errors anywhere.  I run the sendmail server on the
same machine -- all 18 messages are shown as being handed
off without incident to roundup-mailgw.  I recv
roundup-admin mail -- none was forthcoming.  Sendmail logs
show nothing odd.

I only ran it once.  (It is a tracker I'm really using.)  It
was something like the 1st, 2nd, and 4th messages that
didn't do anything.

Want me to test something else?

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That's very, very odd. Something in the chain is failing silently, and 
looking at the roundup-mailgw code I can't see anywhere that I could 
do that. Ultimately if that code broke, the MTA would report an 
undeliverable error. 
 
I can't reproduce the error locally - I think we'll have to add some 
logging to your mailgw. Are you up for that? 
 

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Richard, I am up for fiddling with mailgw; however...

I spent some time trying to replicate this bug (on another,
test tracker).  Unsurprisingly, everything worked exactly as
expected :-(

I would suggest we close the bug; I will make a better
effort to trap
the next occurrence (should it happen).