Deal with Pretalx mail shenanigans

[strugee]

I just set up an alias A record as well as an inbound MX record for pretalx.seagl.org, pointing to Mailu. This is not really great; this domain should not really be in the business of receiving mail.

We should probably:

1. Set the MAIL FROM address in Pretalx's config to a no-reply@ email address.
2. Figure out how to make program@ the default Reply-To address for outbound email sent manually in the Pretalx admin console.
3. Delete the records I just created.

[altsalt]

1. Set the MAIL FROM address in Pretalx's config to a `no-reply@` email address.

Will need to be done server-side.

2. Figure out how to make `program@` the default `Reply-To` address for outbound email sent manually in the Pretalx admin console.

Addressed via https://pretalx.seagl.org/orga/event/2024/settings/mail

Should be tested and confirmed each year.