DomainKeys Identified Mail (DKIM) is an email authentication method designed to detect email spoofing (ie, someone sending email pretending to use fake email under your domain, ie: abc123@yourdomainname.com.sg

We also recommend to add SPF records and DKIM for added protection.

How to setup SPF record for office 365:
https://technet.microsoft.com/en-SG/library/dn789058(v=exchg.150).aspx

How to setup SPF records for google apps:
https://support.google.com/a/answer/178723?hl=en


To check if your domain already have SPF/DKIM records, please click on below link and type your domain
https://www.ultratools.com/tools/dnsLookup


Office 365 (DKIM)

To enable DKIM signing for your domain through the Office 365 admin center

  1. Sign in to Office 365 with your work or school account.

  2. Select the app launcher icon in the upper-left and choose Admin.

  3. In the lower-left navigation, expand Admin and choose Exchange.

  4. Go to Protection > dkim.

  5. Select the domain for which you want to enable DKIM and then, for Sign messages for this domain with DKIM signatures, choose Enable. Repeat this step for each domain.


GOOGLE APPS (DKIM)

To enable DKIM signing for your domain through the Google Apps

  1. Sign in to the Google Admin console.
  2. Click Apps > Google Apps > Gmail > Authenticate email.
  3. Select the domain for which you want to generate a domain key.

    The name of your primary domain appears by default. To generate a domain key for a different domain, select it from the drop-down list.

  4. Click Generate new record.
  5. If your registrar doesn't support 2048-bit keys, change the key length from 2048 to 1024.
  6. Optionally, update the text used as the DKIM selector prefix.

    The selector prefix is used to distinguish the domain key that Google Apps uses from any other domain keys you may have. In most cases, you'll select the default prefix "google". The only reason to change the prefix is if your domain already uses a DKIM domain key with the selector prefix "google".

  7. Click Generate.

    The text box displays the information you need in order to create the DNS record that recipients query in order to retrieve the public domain key.


Office 365 (SPF)
https://technet.microsoft.com/en-SG/library/dn789058(v=exchg.150).aspx


Google Apps (SPF)
https://support.google.com/a/answer/178723?hl=en