Re: Network Delay
Hi
On Wed, Oct 30, 2013 at 09:26:56AM -0400, Roman Gelfand wrote:
> Looking at the tcp stream, below, of a smtp conversation, it appears
> there is 5 second delay before the actual smtp conversation begins.
> Is this normal behavior. If not, any ideas what/where specifically,
> in networking, I should be troubleshooting? No change was done to the
> server or any other machines on the network. This started happening
> all of a sudden.
There are a couple of possibilities for this delay.
Some mail server (exim4 for example, I believe) introduce a small
delay before sending the SMTP greeting. SMTP clients are *meant to*
wait for the greeting before sending SMTP commands, but (apparantly)
many spambots did not. Thus, rejecting email where the SMTP client
was "too eager" turned out to be a decent way of reducing spam. I
suspect that spammers have not learned to obey that standard, so it
may have little effect.
Another possibility is that the mail server attempts to do a reverse
DNS lookup on the source of the connection - but this will usually be
a longer delay
Hope this helps
--
Karl E. Jorgensen
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