I'm looking for suggestions on storing email aliases in ldap. It seems that
sendmail has one schema and postfix a different one. 389 doesn't appear to
support either out of the box. Are there any standardization efforts out there?

Thanks!

Try like below

dn: sendmailMTAKey=testuser,dc=example,dc=com
objectClass: sendmailMTA
objectClass: sendmailMTAAlias
objectClass: sendmailMTAAliasObject
sendmailMTAAliasGrouping: aliases
sendmailMTACluster: ldapter-cluster

sendmailMTAKey: testuser
sendmailMTAKey: tuser
sendmailMTAKey: testu
sendmailMTAKey: test.user
sendmailMTAKey: test_user
sendmailMTAAliasValue: test_user@example.com

sendmailMTAAliasValue: user.tesreplace the cluster name with the one you have mentioned in sendmail.mc file


Once the above entries are added to ldap server, please test using sendmail -bv command and see whether it returns the correct results or not.

Add the server address and basedn to /etc/openldap/ldap.conf file.

Regards
Arpit Tolani