[mailto:owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of Paul Smith
Sent: Thursday, September 01, 2011 9:10 AM
To: Menachem Moystoviz
Subject: Re: Recipient is offline
On 01/09/2011 15:35, Menachem Moystoviz wrote:
Suppose one person (Let's call her Alice) wants to send an email to
another (Let's call him Bob).
Yes, I've seen them around.
However, experience with Google's Gmail service has showed me that
usually, the server gives up after several seconds.
I'm almost certain that's not the case. I would be surprised to see Gmail
tries and gives up only a couple of times in a short period.
Is my sample biased or is this the norm, in violation of the RFC?
The RFC (5321 replaced 2821, by the way), but as Paul points out there's no
normative requirement to try a specific number of times or for a specific
duration, just some guidelines.
Moreover, will Bob receive the mail in my example?
More than likely.
Because this would mean that any user who turns his SMTP server on for
a couple of hours each day would receive his mail.
As long as there's a retry during that window, yes. But that isn't guaranteed.
I'd say that most probably try for 3 days (gives admins chance to fix
their server after a weekend if it broke on the Friday evening). Busy
ones like gmail could try less because they have so much mail, and don't
care as it's a free service. As long as they generate an NDR it's
compliant with the standard.
After some little-known sysadmin trickery I learned a long time ago[*], I
managed to figure out that they do indeed try for at least a couple of days,
though the frequency of retries is not constant. They certainly don't give up
after only a few seconds.
However, if a mail server is online for only a few hours a day, then I'd
seriously suggest getting a backup mail server to accept messages during
the downtime (or putting the main mail server somewhere else with a
better connection), unless you don't really care about getting mail...
I concur, especially if it's one that lets you do ETRN (RFC1985) or some other
demand-based delivery system.
[*] I asked them.