What are your MX records?
A free service to check the MX records for your domain, brought to you by RangerMSP.com - professional service automation software for small/mid-sized IT service providers, MSPs and computer repair shops.
It does a DNS lookup for your domain to see if you have MX records configured and what they are.
Check with your DNS provider and make sure you add appropriate MX records for your domain.
Who is your DNS provider? Often your Domain Registrar but not always.
Who else provides DNS services? Cloudflare is one example, Google has many others.
Need to check your ports? Try My Port Checker!