Adding subdomain in Exchange mail server

For example if currently I have these:

@                MX  mail.abc.com
IPaddress  A     mail
IPaddress  A     autodiscover

You mean that I have to add this one?
xyz.abc.com    MX    mail.abc.com

Am I right?

Yes.

Hi,
In Exchange and Local DNS, you have nearly nothing to do. Locally, Exchange will distribute emails for sub domains directly in mailboxes associated with these emails.

Now, for public DNS, you just have to find the procedure in the admin interface of your provider. It is not a new domain to buy,  just some MX, autodiscover with CName to define.

Hi Thiery, can you clarify which dns records do I have to add?

​I'm ​​​​​thinking of using accept domain in my Exchange server

You do this with abc.com domain registrar or through a DNS panel.

Try this
nslookup -q=soa abc.com 8.8.8.8 as an example, it shoukd report the external party responsible for DNS records of your domain.

One think, first try it locally, to make sure Exchange is handling the subdomain emails correctly.

Using using your abc.com email to send to the subdomain

I'm thinking of using accept domain in my Exchange server 

You can add the subdomain as accepted domain.

For the public DNS zone, you should at least define an MX for your subdomain and an (A) or (CNAME) Autodiscover if some users will use this sub-domain as primary domain.
For exemple,  my provider (OVH) gives me the possibility to create a record as "autodiscover.subdomain.domain.com". This record can be a type (A) or (CNAME). CName that redirects to your actual servers/names, is the better choice, as you will not have to update your actual certificates with the new names to manage.
 
Note that, by default, subdomains are supposed to be managed by the main domain, if records are not found in the subdomain, records of the main domain should be used. But I'm not sure for the messaging aspect.

Please don't use a CNAME for MX record
MX and NS records must never point to a CNAME alias. - https://ns1.com/resources/cname

Echo Andyalder comment, but in this case the CNAME reference was for
Autodiscovery.xyz in CNAME autodiscovery.abc.com.
And is not a threat to the MX/NS as noted AndyAlder.

Exact, MX is never a problem, and not linked to certificate.

an MX will be impacted if the same record is defined as a CNAME
i.e.
somedubdomain IN MX mail.mydomain.com.
somedomain IN CNAME mydomain.com. #to handle web site access

The MX if memory serves could be imperiled based on SMTP process rules, will follow the CNAME record versus the MX.

Dear All, many thanks for your comments. I also have request to add some DKIM/SPF records for this subdomain. Is there any problem when adding these on the main domain? And how to do it?

SPF you use xyz in txt

The dkim, best to use seperate to avoid sharing the private key if it is further separated ..

What do you mean separate? I think the symbol @ points to a main domain, whereas I only need xyz.abc.com
Currently the main domain has this one:
                                


So should I add this one?
                                
or
                                

For SPF, xyz in txt using the middle example, to include the domain on which it is the subdomain.

The dkim you shoukd setup a dkim.xyz.abc.com where you publish the dkim rules for xyz.abc.com only.