It's useful information to guess what the mail servers may be before displaying options to the user.
For example, doing an MX lookup against the domain of firstname.lastname@example.org would show that the domain is hosted on GMail.
Doing an MX lookup against inky.com returns smtp.arcode.com. Now if you do DNS lookups against mail.arcode.com and imap.arcode.com you'll find they both have A records. imap.arcode.com is listening on port 993 (IMAPS) whilst mail.arcode.com isn't listening on any imap port. So you might want to display imap.arcode.com as a possible option.