How to configure mail and SPF in Plesk if DNS is hosted externally?

Question

How to configure host mail and SPF record in Plesk if DNS is hosted externally?

Answer

Create the following records on external DNS:

CONFIG_TEXT: Host Record Type Value
example.com. MX (10) mail.example.com. 
mail.example.com. A <localServer.IP> 
webmail.example.com. A <localServer.IP>

Note: Replace <localServer.IP> with the Plesk server IP address.

If an SPF record exists for a domain, the corresponding record should be created as well:

CONFIG_TEXT: Host Record Type Value
example.com. TXT v=spf1 +a +mx ip4:<localServer.IP> -all

For mail autodiscovery to work it is also required to create SRV records manually on the external DNS:

CONFIG_TEXT: _imaps._tcp.example.com. SRV example.com.
_pop3s._tcp.example.com. SRV example.com. 
_smtps._tcp.example.com. SRV example.com.