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Re: slow email validation problems (was reject vs bounce)

2005-09-14 01:22:55

--On 13. september 2005 10:09 +0100 Paul Smith 
<paul(_at_)pscs(_dot_)co(_dot_)uk> wrote:

We're trying to decide what to do about this. The 'easiest' thing to do
is to accept the message if it's going to take over 30 seconds to
process, and generate a 'bounce' later if necessary - but I don't like
that because of faked sender addresses.

I guess other people here have had the same sort of problems, so are
there any better alternatives?

I'm thinking of generating '250-please wait' multiline response lines
every 30 seconds or so whilst the message is being processed, with a
final '250 OK' or '550 message rejected because of ...' line.

hmm.... "scaling is the ultimate problem", says Mike O'Dell.

If you take 30 seconds to accept a message, and have the default Postfix process limit of 100, you can accept up to 300 messages a minute - or an average of 5 per second.

If you do this, and others follow your example, you're imposing a limit on the SENDING MTA of 5 messages per second (if it's Postfix). If you have large resources on the sending side, you can open up connections until you run out of process descriptors, port numbers of something else - but it's a heavy demand on a busy mail system to increase the average transaction time from sub-seconds to more than 30 seconds.

I hope most of the recipient MTAs for IETF mail don't do this.


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