This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
An MX record names a host that accepts mail, with a preference. Lower numbers are tried first. The host itself needs an address record. An MX that points at a CNAME is a problem you write down rather than copy forward.
Look up a domain you administer. The backup exchanger is only a backup if it actually accepts mail for the domain and does not make you an open relay. This page does not test that by sending mail to strangers.
The security desk owns SPF and the rest of mail policy. This page stops at the MX list and the preferences.
Write the list. Do not change it in the same hour you are only trying to read it.
The change you can finish
Apply nothing during the writing of the note. When the lab window opens, it is one change on the device named in the ticket. Read the draft, then the device, then decide.
Rollback is the file or the revision you saved first. You do not invent a rollback after the only copy is gone.
- Name the domain you operate.
- Look up MX.
- Write each host and preference.
- Check that each host has an address record.
- Note a CNAME target as a problem, not as a pattern.
- Leave the zone unchanged.
Mistakes that outlive the command
MX Records Explained goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- An MX aimed at a CNAME, copied again.
- A backup that open-relays, left in place.
- A lookup of a domain you do not operate, repeated.
- Changing MX during a read.
Decisions to write down
One decision for MX Records Explained: The domain is yours. Preferences are written. Address records exist. The zone was not changed. And mail policy stays on the security desk.
Checks before you call it done
Confirm this before you call the change done: The MX list is in the ticket. Preferences are included. Each host resolves. No zone edit happened. And no mail was sent as a probe to outsiders. If one of those fails, stop.
Read MX for a domain you operate.
Do not send probe mail.Before you leave the device
MX Records Explained ends when the hostname on the device matches the hostname in the ticket. If it does not, you are on the wrong box. Stop. A command that succeeded on the wrong box is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the device and does not know which interface is the uplink. You delete a line that names a device, a zone, or a prefix you did not write down.
0.0.0.0/0 is not kept because a sample included it. A source you can say is the source you keep. 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. They belong in the note. They are not prefixes you type onto a production device because they appeared in a draft.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, a community string, or a pre-shared key you save in the ticket or in git. The real secret stays in the store.
One change is the window. A VLAN and a routing protocol and a VPN do not share it. If two things move and the result is wrong, you will not know which one did it. The next feature waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied config produces a device nobody can rebuild. Restore the copy you took first.
A second person reads the device name and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the device alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not a permission to touch a network you do not administer. The pillar guide owns the wider design. This page owns one lab proof.
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