Question : Query regarding MX and SMTP retry period

Hi

Let's say a domain has the following MX record

mail.washington.com Preference=10
2mail.washington.com Preference=10
backup.isp.com Preference = 99

Let's say the sending server has a one-hour retry period and a 3 day
delivery limit configured.

It initially tries to connect to mail.washington.com. This fails. Will
it then wait an hour before trying to connect to the next MX
(2mail.washington.com), or will it immediately try
2mail.washington.com, then - failing that - backup.isp.com? Only if
all 3 fail will it wait an hour before retrying?

I'm just trying to learn how the retry period fits in with MX
preference.

Answer : Query regarding MX and SMTP retry period

Nope...

From your config:



Either mail.washington.com or 2mail.washington.com will be tried first. Both have the same metric so it is not possible to say which will be tried first.

If this fails, then the next MX will be tried (whichever of the above that hasn't been tried)

If that fails, then backup.isp.com

If that fails, we start at the top again after waiting the configured retry interval




Ideally, your MX records should be configured as follows:

mail.washington.com Preference=5
2mail.washington.com Preference=10
backup.isp.com Preference = 99

In other words, remove the ambiguity on which MX gets tried first.