Can't send email from internal server, same domain name as external.

Question

We have a domain "example.com", hosted externally, for email and a website.  We are thinking of hosting email 'inhouse' and have setup a dedicated subdomain on a 'fixed' IP, "mini.example.com" for AFP services mainly. mini.example.com provides DNS internally, its primary zone is also example.com. All access to the external web goes thru' a modem/router that the server is connected to. We have to set an A record for www access to our website.
In our testing to migrate email, the internal setup works fine, until the switch over.  Now we can receive mail to the mini server, but can't send any out.
We instructed our webhost provider to set the CNAME mail.example.com to point to mini.example.com and created a cPanel MX extry mail.example.com, 10 priority.  Previously, the external host had CNAME as mail.example.com to example.com and MX as example.com, 10 priority.
Since the implementation of the CNAME change, we can't send emails out and they get stuck at the outbox waiting. Client Mail app, says to check for port and SSL and account settings.
Any idea where we went wrong here and what we can do to get emails out? We could go to each computer and point-off the DNS to office IP, but we rather not.
Thanks!

Answer 1

Thank you Camelot and MrHoffman for your replies.
I got in this am to find Mail.app could actually send out emails and I'm stratching my head wondering what happened yesterday.
SMTP server addresss was manually set to mail.example.com for all accounts. In trying to get things to work, the mail setup was redone again by "Accounts", in Systems Preferences, when Login is clicked on, and mail was automatically given a SMTP as mini.example.com instead of mail.example.com.  I'm guessing that that could be where the initial 'inside' problems were, given that it had a 0 answer to the MX query. Or then again I wasn't patient enough.
Just for completeness, and if there's something to learn from here, these are the dig results for example.com as seen from within the office network.
============================
~ dig mx mini.example.com :
; <<>> DiG 9.6-ESV-R4-P3 <<>> mx mini.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1791
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;mini.example.com. IN MX
;; AUTHORITY SECTION:
example.com.                    10800          IN          SOA          mini.example.com. dnsadmin.example.com.example.com. 2011120603 86400 3600 604800 345600
============================
~ dig mx mail.example.com :
; <<>> DiG 9.6-ESV-R4-P3 <<>> mx mail.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36128
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;mail.example.com.                    IN          MX
;; ANSWER SECTION:
mail.example.com.          10800          IN          CNAME          mini.example.com.
============================
~ dig mail.example.com :
; <<>> DiG 9.6-ESV-R4-P3 <<>> mail.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35095
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;mail.example.com.                    IN          A
;; ANSWER SECTION:
mail.example.com.          10800          IN          CNAME          mini.example.com.
mini.example.com.          10800          IN          A          10.0.0.34
;; AUTHORITY SECTION:
example.com.                    10800          IN          NS          mini.example.com.
============================
~ dig mx example.com :
; <<>> DiG 9.6-ESV-R4-P3 <<>> mx example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47951
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1
;; QUESTION SECTION:
;example.com.                              IN          MX
;; ANSWER SECTION:
example.com.                    10800          IN          MX          10 mail.example.com.
;; AUTHORITY SECTION:
example.com.                    10800          IN          NS          mini.example.com.
;; ADDITIONAL SECTION:
mini.example.com.          10800          IN          A          10.0.0.34