Add entries for OX Cloud EU and US

[wrosenauer]

Due to our global business selling EMail-Cloud-Services to several ISPs we need to have (for now) two different configurations (US and EU).
We also rely on Thunderbird's intermediate MX lookup since we do not have any control over enduser's mail domains. Please let me know if there are any concerns. I'm open to discuss them.

[cketti]

You should be able to host the configs at https://autoconfig.cloudeu.xion.oxcs.net/mail/config-v1.1.xml and https://autoconfig.cloudus.xion.oxcs.net/mail/config-v1.1.xml yourself. That way you don't have to rely on ISPDB being available or up-to-date.

We also rely on Thunderbird's intermediate MX lookup since we do not have any control over enduser's mail domains.

Presumably, you're already asking customers to set an MX record. You could also ask them to set a CNAME record for the autoconfig subdomain. This is more work on your part. You have to configure your webserver(s) to handle those domains and request TLS certificates for them. However, it will work with email clients that don't support the MX lookup.
As an additional benefit the autoconfig discovery doesn't rely on the (most likely unauthenticated) DNS lookup for the MX record. K-9 Mail already displays a warning message in this case and makes users confirm the found config. There's a good chance Thunderbird will do something similar in the future.

We prefer the decentralized approach and ask providers to host their own config. However, if that's not (currently) feasible for you, we'd be happy to merge this PR. Let us know how to you want to proceed.

[wrosenauer]

Thanks @cketti , yes, we are aware of the decentralized approach and typically prefer it. As of this moment we host a (mail-)platform but no autoconfig servers. We also try to convince our customers to cover the autoconfig for their hosted domains but quite a few are not able to provide it. But to cover at least some part we are now looking into the MX "workaround" and just these days found out that this is now (since 6 months?) in Thunderbird also available self-hosted.
So yes, please merge these configs for now because we are not able to support self-hosted in short-term but will try to move there mid- and long-term.

[cketti]

This change is now deployed.

https://autoconfig.thunderbird.net/v1.1/cloudeu.xion.oxcs.net
https://autoconfig.thunderbird.net/v1.1/cloudus.xion.oxcs.net