Is @ the same as the IP address for @ in the MX record entry of a zone file?

MX entries specify which server(s) to contact for delivering emails to a certain domain. The "@" refers to the base domain, and not to an ip address.

The MX records have nothing to do with the A records for the same domain, they are completely separate. So if you change the A record for "@", it normally won't affect any MX records.

But if you change the "@" to 1.2.3.4 in an MX record, that means the server it points to (e.g. mx1) will be used for delivering emails sent to [email protected] and not to [email protected]. I think there is no point in doing that, and it probably wouldn't work at all.