Maintaining the subscription list of a mailing list

Why is it important that the subscriber list of a mailing list is carefully maintained?

The reputation of the mail servers through which the mailing list server's e-mails are sent depends on sending as few spam e-mails as possible through these servers and on sending as few e-mails as possible to unreachable addresses.

If the individual mailing lists now each contain several permanently unreachable e-mail addresses, the risk that these outgoing mail servers will end up on blacklists increases. E-mail addresses that are no longer accessible are sometimes also used as so-called spam traps or honeypots and are intended to attract spam. The mail servers that then still send e-mails to these addresses are then reported to blacklists as spammers.

The blacklisting of mail servers can lead to the fact that the e-mails of the mailing lists can no longer be distributed to all list participants, because some mail servers reject the e-mails due to the blacklisting. In addition, the e-mails can often only be delivered with a time delay in this case.
All mailing lists are then affected by these consequences.

In order to prevent KIT's outgoing mail servers from being blacklisted, it is important that the subscriber list of the individual mailing lists is carefully maintained and that e-mail addresses that are not (or no longer) accessible are removed from the list.

What is an easy way to maintain the subscriber list?

Sympa has an automatic mechanism that removes email addresses that have been unreachable for a long time from the list and informs the owners about the deletion. For this purpose, a score is calculated for each address that has been unreachable for several times. This value depends on the number of delivery errors and the type of delivery errors (temporary or permanent). The higher this value, the more delivery errors there have already been for this address.

This automatic deletion mechanism is activated by default for new mailing lists.
As an administrator, you can adjust the threshold values for the actions to be performed on the administration page of the list under "Edit list configuration" -> "Bounces". By default, after reaching the threshold for the first level, the list owners will be informed which addresses are not reachable (anymore) and after reaching the threshold for the second level, the corresponding addresses will be deleted and the list owners will be informed about it.

The thresholds you should enter depend on the number of emails sent through the list per month.

If this is only a few emails per month, you should set the limit for the first level to 8, for example, and the limit for the second level to 12.

If there are many emails sent through the list per month, you could set the thresholds to 15 (1st level) and 20 (2nd level), for example.

If you have a lively discussion forum that sends several emails per day, you can set high limits (e.g. 45 (1st level) and 75 (2nd level)).

If you keep the high thresholds that are set by default, you will have to manually check yourself on a regular basis for which e-mail addresses there are delivery errors and remove from the list the e-mail addresses that have been unreachable for several months.

You can view the scores of each email address on the Administration page of the list under "Bounces". On this web page you can also view the last delivery failures of each e-mail address by clicking on an affected e-mail address and clicking on "View last bounce" on the next page below.

On the delivery errors page you can also manually remove email addresses with delivery errors from the list by selecting the corresponding email addresses and clicking the "Delete selected email addresses" button at the bottom of the page.