In addition to mailing lists DMail provides a bulletin facility. This is useful when you need to send an email message to all users but without the overheads of duplicating and sending the same message to all users. The bulletins are organized as follows:
To produce a new bulletin it is necessary to create a new file containing the bulletin, with a name nnn.txt and place it in the bulletin directory. The bulletin id number needs to be greater than the id for any bulletins already used. The tellpop bulletin command can be used as a quick way of producing a new bulletin thus:
Old bulletins can be left in the directory or deleted periodically. Any user which has not seen a bulletin when it is deleted will not see it at all. In addition to prevent bulletin id numbers increasing for ever the following scheme is used: When DPOP starts up if the bulletin directory is empty then all users will have their "last bulletin read id" set to zero. Bulletins id's can then start at one again.
Using the bulletin facility is in some ways similar to sending an email to a mailing list with everyone on it. However it is much more efficient. For example if you have a system with 20,000 users sending an email to all users involves considerable processing and twenty thousand copies of the message are stored on disk, one for each user. In contrast using a bulletin on the same system completely avoids the processing involved in sending the emails to a list. It also saves only one copy of the bulletin. When each user checks for email they then obtain their own copy of the bulletin which, in general they will delete from the server immediately. However, if they do choose to leave it on the server they then have their own copy just as though it was an ordinary email message.
The message headers for a bulletin message are set as follows: