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Re: Keep Alive Response Codes

2005-09-15 05:02:54

At 10:49 15/09/2005, Tony Finch wrote:

If you want to add keepalives, write an ESMTP service extension.

Unfortunately, the 'critics' of the the 'keepalive' discussion here don't seem to understand the problem..

In an ideal world, we wouldn't NEED keepalives..

In an ideal world, SMTP client users would read RFC 2821 and use the timeouts recommended therein, or at least understand the reason for them and maybe set shorter, but still reasonable timeouts (eg 3-5 minutes)

Yes, we could write an ESMTP service extension, but no one would implement it on the client side, because the timeouts specified in RFC 2821 are sufficient that no keepalive would be needed..

However, people override the defaults set in their SMTP client software, and set the timeouts to very low values (30-60 seconds is not uncommon, even though the standard recommends 10 minutes)

Sometimes the server NEEDS to take longer than the very short non-standard timeout allowed by these client to decide whether to accept the message or not.

So, unfortunately there needs to be a solution which works. I really don't think an SMTP service extension would solve the problem - the problem is system administrators who decide they know better than the standards and set low timeouts. These administrators would also turn off any 'keepalive' SMTP service extension, rendering it useless.

As I've mentioned before, the only workable solution I can think of that doesn't involve a 'keepalive' of some sort involves double transmission of the messages that would cause a timeout. This can't possibly be more efficient for the client than just waiting a bit longer (which is precisely why RFC 2821 specifies the long timeout periods).

I wonder how many system administrators who have set short timeouts have actually looked at how many unnecessary re-sends are taking place because of it.

Paul                            VPOP3 - Internet Email Server/Gateway