Chore: Moved the email ingress method to an env variable (#777) (#806)

* Chore: Moved the email ingress method to an env variable (#777)
* Moved the email ingress method in config to an environment variable
* Updated documentation to reflect this

* Added ingress config to staging env config (#777)
* Re-arranged the order in env configs so that email related configs are together

.env.example

@@ -40,6 +40,15 @@ SMTP_AUTHENTICATION=
 SMTP_ENABLE_STARTTLS_AUTO=
 
 # Mail Incoming
+
+# Set this to appropriate ingress channel with regards to incoming emails
+# Possible values are :
+# :relay for Exim, Postfix, Qmail
+# :mailgun for Mailgun
+# :mandrill for Mandrill
+# :postmark for Postmark
+# :sendgrid for Sendgrid
+RAILS_INBOUND_EMAIL_SERVICE=
 # Use one of the following based on the email ingress service
 # Ref: https://edgeguides.rubyonrails.org/action_mailbox_basics.html
 RAILS_INBOUND_EMAIL_PASSWORD=