DNS Records for separated hosting and mail server

Question

I host my site at a VPS. Because I'm no system admin or sort, I don't want to use my own VPS to host my emails because I lack technical knowledge and expertise to maintain a mail server. I also have a shared hosting plan where I have another domain and use the cPanel and emails perfectly for years without a problem.

So, I was wondering if it would be possible to use my VPS to host my site and my SHARED hosting account to host my emails.

To try it out, on Namecheap DNS settings I made the following entries:

• A Record     | @     | VPS_IP_ADDRESS
• A Record     | www | VPS_IP_ADDRESS
• A Record     | mail  | SHARED_IP_ADDRESS
• TXT Record | mail | v=spf1 +a +mx +ip4:SHARED_IP_ADDRESS ~all
• TXT Record | default._domainkey.mail | v=DKIM; k=rsa; p=*******
• CNAME Record | mail | example.com.
• MX Record        | mail | example.com. 0

However, I think I'm missing something here. Would appreciate your help.

Thanks.

Answer 1

The primary lookup key is the domain name, so for clarity let's swap columns in your zone:

NAME  → TYPE    DATA
------  ------  -------------------------------------------
@       A       VPS_IP_ADDRESS

mail    A       SHARED_IP_ADDRESS
mail    CNAME   example.com
mail    MX      0 example.com.
mail    TXT     "v=spf1 +a +mx +ip4:SHARED_IP_ADDRESS ~all"

www     A       VPS_IP_ADDRESS

Now some problems should become more obvious.

The records for your website are okay – both the bare domain, and the www subdomain, have A records pointing to the web server. However, your mail setup is a complete mess.

The CNAME record

CNAME means "completely alias this subdomain to example.com". In your situation that's 1) undesirable, since it'd add a wrong A record to the mail subdomain; 2) illegal, since you cannot mix CNAME and non-CNAME records on the same subdomain, 3) illegal, because the mail subdomain will be the target of MX, which doesn't allow CNAMEs.

Delete it.

The MX record

When people send mail to [e-mail], they will look for a MX record on example.com – that is, the exact same domain as in the recipient's address. They will not look under some miscellaneous subdomain.

Your current MX record is backwards; it's on the mail subdomain, pointing to the root domain (so incoming mail will never reach the shared-hosting server). You should change it to be the other way around:

NAME    TYPE    DATA
------  ------  -------------------------------------------
@       MX      0 mail.example.com.
mail    A       SHARED_IP_ADDRESS

(Well, unless you want your address to be "[e-mail]"... But I doubt that.)

The "spf1" TXT record

When people receive mail from [e-mail], again they will look for a "spf1" TXT record on example.com, exactly as in the sender's address. So your current record is also in the wrong place: it should be under the bare domain.

NAME    TYPE    DATA
------  ------  -------------------------------------------
@       TXT     "v=spf1 +this +that ~all"

Its contents are also somewhat redundant. You don't need +a, unless you're planning the web VPS itself to be sending mail directly. (But it shouldn't be doing that – it should go through the shared-hosting provider's SMTP server, so that messages can be properly DKIM-signed.)

You also shouldn't need both +mx and +ip4:SHARED_IP_ADDRESS, because your MX record will be pointing to that IP address anyway.

The "DKIM" TXT record

This seems to be correct – assuming you obtained it from the shared-hosting email provider.