SMTP RFC 2821 Retry Interval

November 13, 2007 at 11:03:06
Specs: NA, NA

I have a question about the nature of SMTP. I have a mail exchange server I am responsible for. At present I have one MX record pointing directly to the mail exchange server. This all works fine.

I've read the RFC for SMTP, and from what I can gather, if my server goes down and mail cannot be accepted, the SMTP client trying to deliver the mail should retry at set interval, and retry for a period of time (generally 3-4 days) until either a successful delivery of the mail has been made or a permanent failure occurs (in which case it is obliged to send a report to the returnpath address?,

It is section Sending Strategy in RFC 2821 that specifies that if an SMTP Client accepts responsibility to deliver a message to destination then it has to attempt to deliver more than once and only fail after a reasonable amount of time.

The reason I ask is because if this is true, if the SMTP server goes down, that means I will have at least 2-3 days to get it back up without any loss of service, and I don't need a backup SMTP server listed in my MX details?

If anyone knows what I'm talking about, would really appreciate a response,



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November 13, 2007 at 12:29:33
If your the SMTP server goes down the mail will get delivered eventually when it is back up again but I think you might find people getting a little upset when the mail starts arriving two or three days late.

Depending on how much traffic you handle, you are going to have a backlog that is going to slow down current mail. A backup sever is a good idea.

Most commercial SMTP servers handling hundreds if not thousands of Emails an hour will fail after a few hours as they don't want a backlog either.


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November 14, 2007 at 01:37:22
Hi Stuart,

Thanks for your response, the company is only a small one and they are looking to moving to a Regus building, where they have to take up a new IP address. The move should take 24 hours, from the time the mail exchange is taken offline to the time where it is reachable again. I guess if people follow the RFC, and keep mail for a day or two, there shouldn't be any loss of email?



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