Whitelist Senders and domains in office 365 to bypass Spam filters


Office 365 provides  number of tools to maximize the security to secure corporate information based on unique business and technical needs. When built-in Office 365 filters over qualify suspected SPAM, there are a few simple steps administrators can take to whitelist senders and domains in Office 365 to bypass spam filters. It can be a bad experience for end users when legitimate email is being quarantined or blocked as spam and landing in a quarantine folder.

It’s recommended that you being an admin should review your filters so that critical messages bypass the spam folder and reach their intended recipients

You can leverage a safe sender list or a custom transport rule to bypass spam filtering and prevent legitimate email messages from getting marked as junk. Marking a legitimate message incorrectly as spam by the spam filter is known as false positive.

Whitelist Senders and Domains in Office 365

To whitelist senders and domains in office 365 to bypass the spam filter requires you to perform the following steps.

Whitelist Senders and domains in office 365 to bypass Spam filters

  • Scroll down to the bottom and expand “Allow List

Whitelist Senders and domains in office 365 to bypass Spam filters


  • Click on “Edit” button to add the Allow Sender and Allow Domain list

Whitelist Senders and domains in office 365 to bypass Spam filters

  • Once the users email address is added, click on button to add the users to the safe sender list

Whitelist Senders and domains in office 365 to bypass Spam filters

Emails from safe sender list users will not be checked for spam filters and be delivered to recipients

  • Once the safe sender list of users is configured, next step is to configure the safe sender domain list.
  • Click on “Edit” button to add domains to allowed domain list

Whitelist Senders and domains in office 365 to bypass Spam filters Whitelist Senders and domains in office 365 to bypass Spam filters

  • Once the domains are added, emails from these domains will not be checked by spam filters and delivered to users

It’s important to understand that when you add a safe user or domain to the list, you must know the user or domain is legitimate and will not send you a spam email that can harm business operations. Mostly these lists are being configured for business partners or internal applications when sending an email leveraging another media to deliver the emails to mailboxes hosted on Office 365 or systems leveraging exchange online protection to scan the emails before those are being delivered to end user mailboxes.

Understanding SPF, DKIM and DMARC for Secure Messaging


Email security is the utmost requirement of all organizations to protect confidential data from scammers and cyber criminals. Scammers always seem to find a way to trick end user to get hold of organizational confidential data that is available in the form of emails. Leveraging email systems to improve business productivity and communication puts you in a consistent war against spam, spoofing and phishing.

Being a messaging administrator, you need to plan for security of your messaging systems to secure email data. Apart from antivirus tools being installed on the server, following techniques can be leveraged to secure email messages.

  • Sender Policy Framework (SPF)
  • DomainKey Identified Mail (DKIM)
  • Domain-based Messaging Authentication, Reporting and Compliance (DMARC)

Sender Policy Framework (SPF)

Sender Policy Framework (SPF) allow you to identify which email servers are authorized to send emails for organizational SMTP domain. SPF is added as a TXT record and help prevent spoofing. A spoofed email message is modified to appear as if it originates from a sender other than the actual sender of the message. When a user sends an email, the sending server issues a command in the SMTP message header “From” and include the information of sending server.

Understanding SPF, DKIM and DMARC for Secure MessagingRecipient messaging system refers to SPF TXT record to determine whether a message from your domain is being received from authorized server that are being advertised in your DNS.

If you do not configure authorized servers for your organization that can send emails then the receiving email server can choose to reject the message as SPAM. The reason why the receiving server can reject your message as SPAM is because they cannot validate that the message comes from an authorized messaging server.

SPF record types were deprecated by the Internet Engineering Task Force (IETF) in 2014. Now weo leverage TXT records in DNS to publish SPF information

Configuring SPF in Office 365

If you are planning to leverage Office 365 emails then you need to add the following public DNS TXT record for sender policy framework.

Record Type = TXT

TTL = 3600

Target = v=spf1 include:spf.protection.outlook.com -all

If you are using on premises Exchange server to send emails outside of your organizations then you need the following information for sender policy framework TXT record.

  • IP address
  • Domain Name
  • Enforcement Rule Information

Below is the format of SPF TXT record. SPF TXT record starts with v=SPF1

v=spf1 [<ip4>|<ip6>:<IP addresses>] [Include: <Domain Name>] <enforcement rule>

Let’s assume the public IP address of our exchange 2016 server is and the SMTP domain is msexperttalk.com then the SPF TXT record will be as below.

v=spf1 ip4: include:msexperttalk.com -All

More information on how SPF prevent against spoofing can be found on TechNet.

SPF does not work when you have email forwarding setup on user mailbox. It’s recommended to use SPF in conjunction with other email authentication methods DKIM and DMARC

DomainKey Identified Mail (DKIM)

DomainKeys Identified Mail (DKIM) lets an organization take responsibility of an email message that is in transit and help validate domain identity. DKIM is a more advanced version of Sender Policy Framework (SPF) that helps validate that an email message came from the domain it appears to come from by leveraging cyrptographic authentication. DKIM adds a digital signature to email messages in the message header and authorize your domain to associate or sign its name to an email message. Email systems that receive email from your domain can use digital signature to help determine if incoming email that they receive from your domain is legitimate.

DKIM itself does not directly prevent, filter or identify any spam. It’s recommended to user DKIM in conjunction with SPF to have much better validation of email message

Configuring DKIM in Office 365

Follow the steps mentioned below to configure DKIM in Office 365.

Get-DKIMSigningConfig <Domain Name> | FL *CNAME

Understanding SPF, DKIM and DMARC for Secure MessagingThe output of the cmdlet contains the DKIMsigning configuration for CNAME records.

  • Add the 2 CNAME records in your DNS registrar. Below is the format of CNAME Records

Record Type = CNAME

Hostname = Selector1._domainkey.<Domain Name>

TTL = 3600

Target = Selector1-<Domain Name>._domainkey.<Tenant Name>

Record Type = CNAME

Hostname = Selector2._DomainKey.<Domain Name>

TTL = 3600

Target = Selector2-<Domain Name>._DomainKey.<Tenant Name>

  • Once the records have been added to public DNS, run the following cmdlet to enable DKIM in Office 365

New-DkimSigningConfig –DomainName <Domain Name> –Enabled $true

More details on DKIM can be found on TechNet.

Domain-based Message Authentication, Reporting & Compliance (DMARC)

Domain-based Message Authentication, Reporting & Compliance (DMARC) is an email authentication protocol builds on the SPF and DKIM protocols that add reporting capabilities to allow sender and receiver to improve and monitor protection of the domain from fraudulent email. DMARC policies are published in DNS as TXT record and advertise what an email receiver should do with non-aligned email message received from sender organization.

by default, Office 365 tenant is enabled from DMARC and evaluating messages. DMARC look for the following information in email header.


Authentication-results: protection.outlook.com; spf=pass / fail
(sender IP is x.x.x.x) smtp.mailfrom=sender@domain.com
dkim=none/pass (message not signed OR signature was verified) header.d=SenderDomain;Recipient; dmarc=none / pass

Exchange Online Advanced Threat Protection

Exchange Online Advanced Threat Protection

Exchange Online Advanced Threat Protection

In the modern era, we have seen a steady increase in data security specially the email security against spammer. Spammers are constantly changing the way they send and mask spam/viruses. Microsoft is continuously working to protect their customers against modern era techniques so that customer can enjoy the best in class services. With that being said, On 8-April Microsoft has announced the new advanced robust optional feature to protect against Spam, viruses and malware with Exchange Online Protection. Yes ! I’m talking about new Exchange Online Advanced Threat Protection and I’m excited to deep dive into ATP. Currently ATP is available in private preview only and is expected to be available to commercial customers as optional service by this summer.

ATP will have the following advanced features as optional service.

  1. Protection against unknown malware & Viruses
  2. Real time protection against malicious URLs
  3. URL trace & Rich Reporting

ATP will be available at $2 per user per month for commercial customers and $1.75 for government pricing customers as optional feature.

More details on ATP can be found on Office Blog.