If you have a dedicated IP, you can instruct your clients or recipients to whitelist just that IP. If you do not have a dedicated IP, your emails will be sent from Mandrill's shared IP range. This range is continuously updated as we add more servers for sending.
We do not recommend whitelisting by IP because Mandrill's shared IPs may change without notice and the recipient would be whitelisting all mail from Mandrill. If whitelisting by IP is the only option, the recipient domain should check for the most up-to-date IP information in the TXT record for
spf.mandrillapp.com. On a Mac or Linux, use the following command to get this information:
dig TXT spf.mandrillapp.com
The record is updated when new IPs are added to Mandrill's sending IP range. If a receiving server is whitelisting the range, we recommended periodic checks to ensure they have the current range used by Mandrill.