In a2z, event manager email addresses are added to event configuration, so that the emails like the confirmation letter and statement are sent from their own email domain. Typically one's domain is configured to know what email servers belong to it, and spam detectors can block mailings that they detect as being "spoofed" - sent by one domain as if from another.
Therefore, it is necessary to configure the domain from which one sends emails to add the a2z servers to the known and allowed list.
This is typically done by one's IT department or whomever manages the domain that the emails come from, and the setting they need to update is SPF (Sender Policy Framework) record.
The following configuration should be added to the existing SPF record:
In rare cases a message is returned to say that the spf-a.a2zinc.net causes too many DNS lookups. In this continency, the following alternative can be used:
TIP!! You can check to see if a2z's SPF record has been added to an email domain by using this free tool: https://www.kitterman.com/spf/validate.html