DNS, unlike host tables, allows arbitrary names to represent electronic mail destinations. You can and most organizations on the Internet do—use the domain name of your main forward-mapping zone as an email destination
or you can add domain.
One of the advantages of the Domain Name System over host tables is its support of advanced mail routing.
What is Mail Hub
Mail hub is the powerful central network or machine , to handle all mails . It’s the full set up to handle all request , it may be act as a mediator between sender address and destination address.
The main advantage of using Mail Hub , is that you don’t need to worry about mailer like Send Mail , nor to run it on your own network , you can just connect to a common Mail Hub platform.
Also the advantage are that clients do not need to be continually aware of changes on Mail Hub& Mail queues is on the hub and hub will deal with it, not on the client machine, making the things simpler for client
Components involved in Mail transmission
There are different components involved in an email transmission from sender to recipient, just have a view on it –
1- MUA (Mail User Agent)
2-MSA (Mail Submission Agent)
3-MDA (Mail Delivery Agent)
You can read about above four component – https://afreshcloud.com/sysadmin/mail-terminology-mta-mua-msa-mda-smtp-dkim-spf-dmarc
DNS uses a single type of resource record to implement enhanced mail routing, the MX record. Originally, the MX record’s function was split between two records—the MD (mail destination) and MF (mail forwarder) records.
MD specified the final destination to which a message addressed to a given domain name should be delivered.
MF specified a host that would forward mail on to the eventual destination, should that destination be unreachable.
Is it necessary to have MX Record ?
Even though nearly all mailers will deliver mail to a destination with just an address record and no MX records, it’s still a good idea to have at least one MX record for each legitimate mail destination.
Most mailers, including sendmail, will always look up the MX records for a destination first when there is mail to deliver.
If the destination doesn’t have any MX records, a nameserver usually one of your authoritative nameservers still must answer that query, and then sendmail will go on to look up A records