Previously whenever a mail client connected and authenticated using SMTP, ETRN, ODMR, APOP or POP3 the SMTP delivery IP address was automatically updated to match the client IP address. This feature meant that users with dynamic IP addresses could combine SMTP delivery with frequent automatic connections to inform Mailkeep of changes.
Now this is an option which you can change in your Access and Delivery account page. The checkbox is at the end of the SMTP Delivery Target section.