Is there support for how to have multiple servers for email? I’d like to have two MX for a failover server in the event of something happening to my primary.
Is this possible? Is it documented somewhere?
Hi tjw
Welcome aboard. You can add additional MX records with a suitable priority, manually, or if using the Mythic Beasts DNS API, add a text file to config/dns using TinyDNS escaping. Just ask if you want pointing at the file format.
As the MX are only receiving I don’t think that you have to worry about altering SPF, DKIM or DMARC settings — Sympl will be unaware of the diversion.
I used to run with backup MX when broadband connectivity was less reliable but prefer not to nowadays as spam/config control is easier with one target. Saying that, I came a cropper with my last ISP with a massively long loss of service which I never expected short of a nuclear strike on London. 
Welcome @tjw!
There’s no direct support for things like load balancing, backups of failover with Sympl, although it would be theoretically possible, it would likely be very complex.
If you want a fallback MX service with Sympl, you can use a separate service like the one with Mythic Beasts, which works by adding the ‘backup’ servers with a lower priority (confusingly, with a higher priority value in DNS), which then will de-queue the mail when your server is back online.
As @alphacabbage1 mentions, there’s no configuration for that needed with Sympl, as it just sees normal mail coming in which has an extra network hop.
Thanks for the welcome!
And thank you for the support.
I think for now I will just stick with the one Sympl server and then if required in the future I could add a fallback MX server (either hosting my own or using Mythic Beasts)
When legitimate systems send email, they choose the lowest cost MX and if that’s not available, switch to the next.
When spammers send email, they generally send it to every MX.
This has the effect of doubling the volume of spam that is sent.
However, perhaps this has a benefit. If you have two MX, you could filter any messages sent to both of them as being probable spam.