SPF stands for Sender Policy Framework. A SPF record includes all email servers which are allowed to send emails with your domain. This allows email servers to easily determine if an email was sent from one of your trusted servers or by someone else.
A SPF record is a TXT record and may look like this:
v=spf1 a mx include:_spf.office.com ip4:84.233.65.34 ~all
v=spf1 specifies the SPF version
a specifies to include the IP the domain resolves to
mx specifies to include the mailservers in the MX records
include: specifies to include the SPF record it refers to
ip4: specifies an IPv4-address to include
ip6: specifies an IPv6-address to include
~all/~all/+all/?all specifies the SPF policy
Make sure you include all your email servers you send email with. This includes your email provider, software you send newsletters with and more. Contact support if you are not sure what to include.
Policies
~all is a softfail and tells mailservers to handle the email with extra caution.
-all is a fail and tells mailservers to reject the email.
?all is neutral and lets mailservers decide on their own.
+all is a pass and tells mailservers to let the email go through.
Lookup limit
SPF records have a lookup limit to prevent slow processing and long DNS lookups. Only 10 lookups are allowed. This includes nested lookups. The following parameters are included in a lookup:
a
mx
include:
Each entry counts as one. If the record behind include: also contains one of these above, it will be included in the lookup limit.
Email delivery may fail if the lookup limit is exceeded.