Connect Application: Implementing SPF for Outbound Email Delivery

Document created by user.oxriBaJeN4 Employee on Apr 14, 2016•Last modified by user.m8lcBwVNwY on Feb 21, 2018
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Applies To...

 

This page applies to new clients connecting with Mimecast using the Connect Application. If you are not using the Connect Application, click here.

 

Overview

 

Sender Policy Framework (SPF) is an open standard for email authentication. It validates the connecting IP address, by looking up the SPF / TXT record in DNS for the domain in the envelope MAIL FROM or HELO/EHLO. By adding our _netblocks.mimecast.com entry to your SPF / TXT record, you ensure we are allowed to send mail for your domain name. Mail Transfer Agents (MTAs) can verify SPF for inbound emails if the sender publishes DNS entries for them in their domain records.

 

Implementing SPF for Outbound Email Delivery


To ensure a successful implementation of SPF with Mimecast, include a comprehensive list of our outbound IP addresses in your DNS SPF record. This is a long list (24 distinct IP4 ranges at the time of writing) and new ranges may be added in the future without notice. However, you can ensure your record is always up to date by including the "xx._netblocks.mimecast.com" statement.

 

To determine what "xx" is for your region, refer to the table below:

RegionRecord
Europe (UK and Jersey)v=spf1 include:eu._netblocks.mimecast.com ~all
North Americav=spf1 include:us._netblocks.mimecast.com ~all
South Africav=spf1 include:za._netblocks.mimecast.com ~all
Australiav=spf1 include:au._netblocks.mimecast.com ~all
Global (includes all the above)v=spf1 include:_netblocks.mimecast.com ~all

 

Some typical examples are suggested below as a starting point for constructing an appropriate record:

ScenarioDescriptionExample
Simple CaseRelaxed configuration for customers which only send external mail for a given domain via Mimecast."v=spf1 include:_netblocks.mimecast.com ~all"
Strict CaseFor customers wishing to implement a strict SPF reject for unmatched requests, we strongly recommend testing with the relaxed syntax first."v=spf1 include:_netblocks.mimecast.com –all"
Customers with an Existing SPF Record for a Given DomainIf you have an existing SPF record representing a range of possible senders, these examples show how you can include Mimecast as a legitimate sender.
Old"v=spf1 mx ~all"
New"v=spf1 mx include:_netblocks.mimecast.com ~all"
Old"v=spf1 ip4:192.0.2.0/24 ip4:198.51.100.123 a -all"
New"v=spf1 ip4:192.0.2.0/24 ip4:198.51.100.123 a include:_netblocks.mimecast.com -all"
Customers with an Existing SPF Include Record for a Given DomainIn all cases, customers with existing SPF records should review their entries to ensure Mimecast servers are referenced exactly once. Any previous Mimecast references should be removed in favor of _netblocks.mimecast.com. Customers using a domain include a mechanism to refer to a DNS entry which already references _netblocks.mimecast.com, need take no further action.
Old"v=spf1 ?include:example.com -all"
New"v=spf1 ?include:example.com include:_netblocks.mimecast.com -all"
View the Connect Application: Setting Up Your Outbound Email page for more information on updating your SPF records via the application.

Creating the DNS Entry

 

If you wish to implement SPF for your domain, you'll need to create a corresponding TXT DNS record. By adding our IP Ranges to your TXT / SPF record, you ensure Mimecast is allowed to send mail carrying your domain name.

 

To create a DNS record:

  1. Update the SPF records for your domains with the information displayed in the application under SPF Record, as shown below:
    SPF Record Entry
    Only use the SPF record displayed in the application, as there are regional differences (i.e. "eu" for Europe in the above image). The regional records are also listed in the "Implementing SPF for Outbound Email Delivery" section above. If you're not the person responsible for this task, click the Share link to send an email containing the required detail to someone who is
    1. Log on to your Domain Registrar.
    2. Update / replace each domain’s SPF record to specify us as the authorized outbound service.
    3. If all email for your domains will be routed via us, remove all previous SPF records.
    4. Other outbound sources for your domain may require a combined SPF record. In this instance, ensure you include the Mimecast "xx_netblocks.mimecast.com" entry before creating a mail flow connector. To determine what "xx" is, refer to step 1 above.
      See the "Implementing SPF for Outbound Email Delivery" section in the Configuring DNS Authentication Definitions and Policies page, and the Implementing SPF for Outbound Email Delivery page for additional information.
  2. Optionally test your SPF record:
    1. Navigate to Platform | Set Up Your Outbound Email in the Connect Application.
    2. Select your domain from the Record to Validate drop down menu.
    3. Click on the Validate button. One of the following messages will display:
      • A green tick confirms the SPF record is valid.
      • A red exclamation confirms the SPF record is invalid.
    4.  Click on the More or Less links to view further information about the SPF record and toggle the display.
      This step performs a TXT record lookup and validates the SPF record entry. You can have more than one mechanism (IP/Host), but Mimecast must be the first one listed.
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