about the use of Multidropmailboxes

Support knowledgebase (rsimai_imap_multidrop)
Applies to

eMail Server: Version 2

Situation

You like to poll mails from a multidrop mailbox from your providers server using the eMail Servers Fetch Mail function.

Procedure

Create a new (dummy-) user, who receives the mail from the multidrop account.
Enter this user as recipient for the mails of the multidrop account, configured by fetchmail.
Log in as this user for the configuration interface and create procmail rules like this:
if the recipient contains USER-XY forward to the user USER-XY@MY_MAILSERVER
Should this mail be received by more than one recipient you have to enable the checkbox for
Copy filter. Even if this filter matches...
You have to setup one rule (filter) per user!
If the mails should not be collected in the dummyusers inbox, it is possible to delete them with a last filter rule
Be careful with this: also not delivered mails will be erased in this case!

Our installation support is not able to offer help concerning problems in relation to multidrop mailboxes! Please read the next paragraph.

Background and problems

A multidrop account is a simple POP3 (Post Office Protocol) account which stores the emails for the whole domain. The mails have to be fetched from this with POP3, they have to be distributed at the target system. Since the SMTP (Simple Mail Transfer Protocol) is already finished at the providers server, some information is lost. The most important has been the address of the recipient, the so called Envelope Recipient address.
An email consists of Envelope, Header and Body. The envelope is generated while transferring the mail from MTA (Mail Transfer Agent) to MTA. This is comparable with a postmark on a letter. Once, the mail is delivered, the envelope has been removed. Normally, this shouldn´t cause problems because the mail is sent from one user to another. In this case the recipient of the envelope is similar to the recipient of the header (To:). Otherwise if the user is member of a mailing list, the recipients address will be To: mailinglist@domain.com for every user who is a recipient of this mail. The 'real' recipient is transmitted during the transport using the SMTP command RCPT TO. If the mail reaches its destination, this information will get lost.
Of course, it won´t get lost at all, otherwise no software would be able to distribute mails fetched from multidrop mailboxes. The recipients address is left as 'tracks' behind in terms of Received: lines in the mail header. From this it is possible to reconstruct the recipient. Unfortunately these information is not standardized, any MTA can add thess lines as wanted.
Therefore mistakes while delivering mails are always possible. If possible multidrop mailboxes should be avoided!

You may also find explanations about this at in the manpage man fetchmail (if you have installed fetchmail). You have to look for the term 'THE USE AND ABUSE OF MULTIDROP MAILBOXES'
See also:
o fetchmail: Collecting Mail from the Provider

Keywords: IMAP, EMAILSERVER, MULTIDROP, FETCH, MAIL

Categories: SuSE Linux IMAP Server

SDB-rsimai_imap_multidrop, Copyright SuSE Linux AG, Nürnberg, Germany - Version: 21. Aug 2001
SuSE Linux AG - Last generated: 29. Aug 2001 by rsimai (sdb_gen 1.40.0)