SPF Policy - Allow a specific IP Address

In theory you could create a new SPF rule. enable advanced. set the rule config to none or fail.. then under message attributes add the IP and select IS .. then give it a main action and such.  

then add it above your existing rule and save order//

However this is NOT recommended and requires the correct envelope sender ips and header information.

The recommended fix is to have abc.com fix their dns/txt  :)

As per the RFC.

SPF relays on the HELO identity of the client, or the Mail From Identity (aka the envelope sender)  the DNS name is then looked up resulting in the host dns information.  

section 3 : https://www.ietf.org/rfc/rfc4408.txt  

provides the basic reverse look up information, and section 3 has the requirements for a dns entry.  your v=spf delegation must resolve properly.

"
   Domain owners wishing to be SPF compliant must publish SPF records
   for the hosts that are used in the "MAIL FROM" and "HELO" identities.
   The SPF records are placed in the DNS tree at the host name it
   pertains to, not a subdomain under it, such as is done with SRV
   records.  This is the same whether the TXT or SPF RR type (see
   Section 3.1.1) is used.

   The example above in Section 3 might be published via these lines in
   a domain zone file:

      example.com.          TXT "v=spf1 +mx a:colo.example.com/28 -all"
      smtp-out.example.com. TXT "v=spf1 a -all"

   When publishing via TXT records, beware of other TXT records
   published there for other purposes.  They may cause problems with
   size limits (see Section 3.1.4).

"


You should not be making this kind of rule to accommodate a domain that has invalid / bad dns or has incorrectly set up their txt record.