As long as the system pointed at by the MX record has an A record itself, then yes.
For example: example.com
can have a MX record pointing at mail.otherdomain.com
. As long as the name mail.otherdomain.com itself is resolvable to an IP address, this is a valid configuration for example.com
.
Strictly speaking, mail.otherdomain.com
should be an A record with the IP address in order to be RFC-compliant. But this A record will be in the otherdomain.com
domain, not in example.com
.
Addressing your example, in order for bob@example.com
to be a valid email address, mail.otherdomain.com
needs to be configured to handle inbound mail for bob@example.com
.