We have (at least) two SMTP servers available to us for sending mail, in fact we have way more than that as we have two ADSL connections from different ISPs (hence two SMTP servers from them) and we also have two hosting services separate from the ISPs and they too provide SMTP servers.

Is there any way that we can use these to provide some redundancy when sending mail from Evolution? At present I can't see any really easy way to do it as Evolution doesn't really allow for the use of more than one SMTP unless you manually change accounts.

I run postfix on one of the machines here, I could point Evolution at postfix for sending mail, can one tell postfix to try an alternative SMTP server if the main/default one is down?

It feels like the MX records for the 'smarthost' that we send our mail to (both from Postfix and Evolution at the moment) should provide this but I'm not convinced that it does.

E.g. the mail relay I'm using for my local postfix is relay.mail.gandi.net and that doesn't return any explicit MX records in response to a query.

The mail relay used by evolution is provided by my hosting at TsoHost and is mail.isbd.net, that does have an MX record:-

chris$ host mail.isbd.net mail.isbd.net is an alias for isbd.net. isbd.net has address 188.65.115.75 isbd.net mail is handled by 0 isbd.net.

I can manipulate the zone file for isbd.net but I'm not sure if that will actually do what I need. Can anyone help/elucidate/point me somewhere useful?

A bit of Googling suggests that maybe Postfix's fallback_relay is what I need but I'd like to find a tutorial/howto because the basic manual is a bit concise shall we say.