SOA (Start of Authority) record
This defines general parameters of the Name Service for a domain:
- hostmaster - email address of the domain administrator
- Primary DNS - primary DNS nameserver for your domain
- Time To Live (TTL) - This refers to the default time to live, or how long between queries for new information other nameservers can make. This setting is what affects DNS propagation time the most, as many nameservers are set by default to use 86400 (24 hours).
- Refresh Time - This is the refresh cycle in seconds. In every refresh cycle the slave server requests updates from the master (primary) nameserver.
- Retry Time - Retry cycle which means that the slave server should wait before asking the master server again in case master server doesn’t respond.
- Expire Time - This is the time for slave server to respond to queries of client for the expiration time if master server fails and has to be up and not getting up. After this period slave server also fails to solve the queries of clients and sits idle.
"A" records are the address or "actual" mapping of hostnames to IP addresses. Literally: yourdomain.com = 10.129.40.8
Alias another host name to an existing A record. Often used for the "www" hostname part of a URL. www.yourdomain.com = the A record for yourdomain.com
MX records define where mail for a domain should be delivered. You can have more then one MX record with different preference, smaller number stands for higher preference. If mail server with higher preference will not respond, then the mail will be send to the second mail server with lower preference( higher number)
Much more detailed information about DNS record types can be found at this link.