Messaging Server: mail and mailalternativeaddress attributes must be unique

Question

Email addresses for a given User Directory must have unique mail
and mailalternativeaddress
attributes.
<P>
Messaging Server uses the following two attributes to search for email
addresses in the User Directory:<BR>
<P>
<OL>
<LI>mail
<LI>mailalternativeaddress
</OL>
<P>
Each email address in the User Directory must have unique entries for these
two attributes. If a given email address appears twice in the User Directory,
the Messaging Server will display an error message and will not deliver the
email to either address. In the case where a user wants email that is
addressed to one email address to go to other email addresses as well (e.g., if
a user has multiple accounts), you would need to create a group for that user
and add the other email addresses to the group.
<P>
<B>Additional Notes:</B>
<P>
<UL>
<LI>Administration Server 3.x and 4.x have various mechanisms for
reducing the likelihood of user error when creating email accounts.
<P>
<LI>Administrators of Directory Server 4.x servers should also be aware that
the mail and
mailalternativeaddress
attributes must be unique to prevent collisions between those two attributes.
<P>
The uid uniqueness plugin maintains uniqueness within attributes, but not across attributes.
Using this feature for both attributes cannot fully prevent address collisions.
<BR><P>
For example, a user could theoretically enter duplicate values for the
mail and
mailalternativeaddress attributes:
<BR>
<P>
mail: [email protected]
<BR>
<P>
mailalternativeaddress: [email protected]
<P>
Although the server would initially accept this value for both attributes, it
will post an error message later when it processes an email addressed to this
address.
</UL>

Answer 1

What does “I overwrote the information in Accounts” mean? What exactly did you do? More info, please.
Deleting a mail account (which i not the same as overwritting the account information) causes all your mail stored in that account’s mailboxes to be removed from the computer as well, and you you were warned that this would happen by an alert similar to this for Mail 2.x (I don’t know what the exact wording is in Mac OS X 10.3):
Remove Account
Are you sure you want to remove the <AccountType> account "<AccountName>"?
This will permanently delete the account setup information, mailboxes, and messages from your computer. Messages stored on the mail server will not be affected.For IMAP-type accounts, this is not a problem because mail is stored on the server. If you deleted a POP account, however, your mail has certainly been wiped out from the computer, not just moved somewhere.
To prevent that from happening, you should have moved your mail to custom “On My Mac” mailboxes instead of leaving it in the account’s mailboxes. Actually, using the account’s Inbox and Sent mailboxes for archiving purposes is a bad idea regardless — see Overstuffed mailbox is unexpectedly empty.
If the POP account was configured to leave the messages on the server for some time, setting up the account again would cause any messages still on the server to be downloaded again, just like for IMAP accounts, but this would only work for received mail that has not yet been removed from the server.
If the messages are not on the server and you don’t have a backup (which you should have made before doing something like that), you may try to salvage as many deleted mbox files as possible with a data recovery tool such as Data Rescue II or FileSalvage (the files to be recovered would be different in the case of Mail 2.x). Stop using your computer right now if you want to try that, as anything you do with the computer may cause the deleted files to be overwritten.