Exim - Step1: DNS, SPF, DKIM

Create ssl cert
mkdir /etc/exim/dkim
cd /etc/exim/dkim
openssl genrsa -out /etc/exim/dkim/dkim.key 2048
openssl rsa -in /etc/exim/dkim/dkim.key -pubout > /etc/exim/dkim/dkim.pub
cat /etc/exim/dkim/dkim.pub
Add to your zone dkim/spf records
$ORIGIN .
$TTL 3600               ; 1 hour
domain.com              IN SOA  ns1.domain.com. support.domain.com. (
                                1	   ; serial
                                7200       ; refresh (2 hours)
                                3600       ; retry (1 hour)
                                43200      ; expire (12 hours)
                                3600       ; minimum (1 hour)
                                )
                        NS      ns1.domain.com.
                        NS      ns2.domain.com.
                        A       123.123.123.123
                        MX      10 mail.domain.com.
                        TXT     "v=spf1 mx -all"
                        SPF     "v=spf1 mx -all"
$ORIGIN domain.com.
*                       A       123.123.123.123
ns1                     A       123.123.123.123
ns2                     A       123.123.123.124
mx                      A       123.123.123.123
mail                    A       123.123.123.123
mail                    TXT     "v=spf1 a -all"
mail                    SPF     "v=spf1 a -all"
_adsp                   TXT     "discardable"
_domainkey              TXT     "t=y; o=~;"
dkim._domainkey         TXT     ("v=DKIM1; k=rsa; t=s; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAt1DbQSO38LMJ323FeC"
                                         "uNuVVmxPxGA+IfZScII8sgiV93y52MXHL42rLdJMACmNxEd0VOlKluN95+0QABh"
                                         "IsYaxx0va0FLawMllFiV0u1Ur/IcEvQ8hydY1JUrczKWABO5heyZ1KniGccI2lB"
                                         "5YDhk6F4XnnOVlkQQSPCof//yQzBaoJy4sYWCnshcqtd1y5gWh0sS2JKGVJOp49"
                                         "1QIDAQAB")