1. Open the terminal and type openssl

2. To generate a private key type:

openssl genrsa -out private.key 1024

 3. To generate a public key from the private key type:

openssl rsa -in private.key -pubout -out public.key

4. Find the folder that contains your public key and open it. It should look something like the below.

5. Manually convert the highlighted text above to a single line ie. remove the spaces between new lines. 

To create the DNS record you will have to specify the Name, Type and Value of the DNS record.

The DNS record Name will look like this:

selector._domainkey.domain

or like this if your DNS provider automatically appends your domain name:

selector._domainkey

Where the "selector" is defined by you and can be called anything, for example the date, device or service that will sign the emails.

For example:

20180719._domainkey.redsift.io

The DNS record Type is TXT.

The DNS record Value should look like the below. The part in bold is copied from the generated public key file:

“v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDg9/gR+3J0mmugLjhpYOfQK9ytkEKnXM0kVdpu0UoykSPK7ChD+nRxFJbN2cxtvu8GrCNQwPTKbC0jimaSi0V2j3JndnRrECuYCqeZYcRmw2lYs18QnmJRfCpweKoaGtv9zERCkeHwLcTaLkrSHrRDf58WgERg8x/4ipBPIyZufwIDAQAB”