Ref: http://faq.domainmonster.com/dns/srv/

What is an A Record?

An A-record (address record) maps a hostname to an IP Address.

For example you may want to add an A-record for the hostname "www" and IP address 217.28.124.132 so that www.yourdomain.com resolves to the IP address 217.28.124.132 where your website is hosted.

What is a CNAME record?

A CNAME (canonical name) record maps a host name to another hostname or FQDN.

For example you may want to add a CNAME record for hostname "wwww" to "www" so that anyone mistyping an additional "w" in your website address will still get to the site at www.yourdomain.com.

You could also add a CNAME record for hostname "search" and FQDN "www.google.com" so that anyone visiting search.yourdomain.com would be presented with www.google.com.

What is an MX record?

An MX record comprises a FQDN and a priority. The priority is simply a number which is used to choose which mail server to use if multiple MX records exist for a domain name. A mail server trying to send an email to you will always try the lowest number priority first.

Additionally an MX record has a host name to allow email addresses with subdomains. The hostname is usually left blank to specify the mail server for the domain name on its own.

If you have a mail server at mail.somemailserver.com and you want to add this for your domain name mydomain.com, you would add an MX record with a blank hostname, an FQDN of mail.somemailserver.com, and a priority, e.g. 10.This record would mean that any emails addressed to @mydomain.com would be delivered to the server at mail.somemailserver.com.

If you had a backup mail server that you only wanted mail delivered to in case of a problem with your main mail server, you would add another MX record with an FQDN of mail.someothermailserver.com and a higher priority number( e.g. 20.)This record would mean that any emails that were addressed to @mydomain.com which could not be delivered to the server at mail.somemailserver.com would be delivered to the server at mail.someothermailserver.com.

Adding a hostname into the MX record simply means that you are specifying the mail servers for a subdomain.For example adding an MX record for hostname "london", FQDN mail.mylondonmailserver.com with priority 10 would mean that any emails addressed to @london.mydomain.com would be delivered to the mail server mail.mylondonmailserver.com. It would not affect any emails addressed to @mydomain.com.

What is a TXT record?

A TXT (text) record is used to hold some text information. You can put virtually any free text you want within a TXT record.

A TXT record has a hostname so that you can assign the free text to a particular hostname/zone. The most common use for TXT records is to store SPF (sender policy framework) records and to prevent emails being faked to appear to have been sent from you.

What is an NS record?

An NS (name server) record allows you to delegate a subdomain of your domain to another name server.

For example you have the domain mydomain.com which is using the Domainmonster.com name servers. You decide that you want your own name server (myns.mydomain.com), for which you have already added an A-record, to look after the DNS for a subdomain on your domain: extranet.mydomain.com.

To do this, you would add an NS record for hostname/Zone "extranet" with the name server address "myns.mydomain.com". If someone therefore wants any DNS information about extranet.mydomain.com, our Domainmonster.com name servers will send them in the direction of the server at myns.mydomain.com.

What is an SPF (sender policy framework) record?

An SPF record is a Sender Policy Framework record. An SPF record is actually a specific type of TXT record.

An SPF record is used to stop people receiving forged email. By adding an SPF record into your DNS configuration any mail servers receiving email, that is allegedly from you, will check that the email has come from a trusted source. The trusted sources are provided by the SPF record that you set up.

More information on SPF records can be found on the Open SPF website.

There is also an SPF Wizard which helps you to create the SPF/TXT record for you.

What is an SRV record?

An SRV record is an advanced type of record which allows you to specify services that you have on your domain. Use an SRV record if a certain application or piece of software requires it.

For example, you might want to specify that you have FTP access on your domain. You could use a CNAME to create a subdomain, but this would only tell people the address of the server. An SRV record will tell people the following information in addition to the address:

The Service Name (e.g. _ftp)The Protocol (e.g. _tcp)The Port Number that this service is on (e.g. 21)The Priority (An arbitrary number which tells people which record to pick if you have several SRV records with the same Name and Protocol)The Weight (Another arbitrary number which tells people which records should be used more often if you have several SRV records with the same Name and Protocol)

Ref: http://faq.domainmonster.com/dns/srv/