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Comment by t0astbread | Hacker News Reader

How does that work exactly? Do you set up your server as higher priority MX and the external provider as backup and then configure your server to relay outbound mail through that other service? And all your server has to have is a valid certificate while DKIM/RDNS/SPF get handled by the external service?

Is there anything to watch out for (e.g. w.r.t. bounce mail) in this setup?

Edit: Maybe you don't even have to set up an MX record for the external provider (unless you want to use it as a fallback for incoming mail).

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That's exactly how it works, although you don't need an external backup modern email servers will retry for many days before returning a undeliverable notification if a valid MX record exists. With email receiving and delivering email are two separate tasks that don't need to be done by the same service.

For example I use Amazons SES. They have SMTP credentials you plug into your server and you add the DKIM and SPF txt entries to your DNS. The only thing that points to your own server is the MX record. Gmail will re-write emails to be FROM gmail while others may allow you to do similar to SES.

You don't actually need a valid cert or IPv6 to receive email, everyone only cares about the sending side of things.

Amazon will want to know what automated systems you have to deal with bounces and complaints to protect their service but that's about it

I was thinking of the case where your server has to send out bounce mail but I guess if it's configured right, it should also just relay that.

Yup bounce emails are routed just like any other email so they go through the relay. This is actually one of the gotcha's when using fetchmail, you can accidentally send out a lot of unintentional bounce emails from an invalid server if you are not careful.

It's just like doing bulk mail through a third party, except now you're sending your regular mail through them too.

MX records are used to figure out where to deliver mail so you would leave those pointed at your own mail server, no need to set up any MX record pointed to the 3rd party.

You would need DKIM/SPF, etc for sender verification pointed at the 3rd party.

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