I hope this helps someone:
There were two things that I needed to do to get this working:
on Godaddy - email routing: I had to change this to "LOCAL MAIL EXCHANGER"
Cloudflare:
I had to set up two records on CLOUDFLARE in order for this to work
#1
Record type: MX
domainname.com
mail.domainname.com
1 hr
DNS only
#2
Record Type: A
mail
xx.xxx.xxx.xx (IP ADDRESS of SERVER)
Auto
Proxied
Worked!
Prior to this, as mentioned in the question, I had set up the DNS in GoDaddy's WHM (set the name servers) and the created an A record pointing to the server in the DNS Management tab for the domain.
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