Dkim-add-domainkey

Create a DKIM key for a domain

Create a new folder and cd into it:

mkdir -p /etc/opendkim/keys/mydomain.com
cd /etc/opendkim/keys/mydomain.com

Generate key:

opendkim-genkey -r -d mydomain.com

Delegate access to the opendkim user and group to access the key:

chown opendkim:opendkim default.private

Reference the key via OpenDKIM KeyTable:

vi /etc/opendkim/KeyTable

Add line to the file to define your selector. In this example, we will call the selector default, but if your domain requires multiple DKIM keys, ensure you make this unique. You can modify the file by pressing i to enter insert mode in vi:

default._domainkey.mydomain.com mydomain.com:default:/etc/opendkim/keys/mydomain.com/default.private

Open the SigningTable file via vi

vi /etc/opendkim/SigningTable

Add the following line to the file by pressing i to enter insert mode (changing default if specified a different selector earlier on):

mydomain.com default._domainkey.mydomain.com

/etc/init.d/opendkim restart

Update DNS:

cat /etc/opendkim/keys/mydomain.com/default.txt

Create a new TXT record, name default._domainkey or default._domainkey.subdomain with the value between the quotes (don't include the quotes), e.g.:

v=DKIM1; h=sha256; k=rsa; s=email; p=ABCDEFG.....