The most possible reason why you can't send or receive emails could be because the MX records are not correctly set for your domain.
If you signed up for Business Email with a domain using another Name server provider, you will need to set up the MX records for your domain as per the table below:
Once the MX records are added, please add the below SPF/TXT record as well for your domain:
|v=spf1 include:spf.titan.email ~all
Feel free to knock on our door by writing to us at firstname.lastname@example.org in case you need any assistance with configuring these records.