Email rDNS and SPF

I set up rDNS for domain.com so that the IP uses sub.domain.com.

Do I add SPF records to domain.com or sub.domain.com so that domain.com can send emails?

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So it needs to be done for both? Or only for #2. your domain? This is for emails sent through the server only with an @domain.com I set in the web script in xenForo and rDNS set to sub.domain.com for the server IP. Or would you recommend setting both regardless?

My server also has 2 IPs. I assigned Website A to IP A but it's sending emails through IP B instead. What would I need to ensure that Website A sends emails through IP A?

Custom config has IP B assigned to SECOND_IP.

In my ssl domain config I found IP B (not sure why it was there but my guess is through a nginx upgrade)

Code (Text):

 server {
   listen   IP B:80;

Code (Text):

server {
  listen 443 ssl http2;

I changed IP B to IP A here and restarted NGINX. Is that enough or is there something missing?

It doesn't work:

Code (Text):

sub.domain.com: Sender not authorized by default to use 'nginx@sub.domain.com' in 'mfrom' identity

 

I also added IP A here and restarted nginx but the server still sends emails through IP B.

 

How would I change the main server IP?

My first IP was IP A which I thought was the main server IP. I had added IP B via SECOND_IP.