A list is changed from an open to a closed subscription model to restrict subscribers to an approved group of users. This is a significant change that requires advance preparation. Users will not be able to subscribe directly, so moderators or administrators will need to be available to add subscriptions, update email addresses, etc. If the list already used moderated message posting, existing moderators need to learn how to moderate subscription requests. If there were no moderators, at least one moderator will have to be added at the time of the change. There may be legacy subscribers on the list who will have to be manually removed. As with any new restriction, it's best to take a proactive approach and provide notice and explanation before enacting the change so that list users are prepared. This includes telling current subscribers that they will no longer be able to change their email address by email, but will have to login or submit the emailed request to the moderator.

A list is usually changed from a closed to an open model because the process of approving subscribers has become onerous or because it is decided that the list doesn't need to be controlled quite this tightly. When this kind of change is made, the list is usually still kept private (i.e., closed to public subscription requests), and restrictions on posting and archive access are usually retained.

When a list loosens it's posting restrictions it's because it wants to be more inclusive. It expects an influx of posts by users who were formerly not allowed to post because they were further from the core of the group served by the list. Although this may inject fresh energy into the list, it also tends to make the list content less focused. This may irritate certain members of the list who prefer the list to remain focused, even if this means interest in the list is dwindling and list posts are tapering off. Sometimes these users will form a spin-off list that they can keep private, and cross-post to the larger list or abandon it altogether. In cases where a list is not being used as intended because it has dwindled to a few users focused on a narrow agenda, opening the list to more users may bring the list back on course.

To view a table that shows how the different settings affect different levels of users, see Posting access matrix.

Lists usually tighten posting restrictions because they are being overwhelmed with off-topic content or posts by inexperienced list users asking questions whose answers are probably in the FAQ or archives. This may also be a list where posts by unauthorized users were being sent for moderation (until the deluge of moderation requests reached a critical mass and overwhelmed the list's moderators) and are now being rejected outright. Either way, users who were once able to post will now find their posts rejected or sent for moderation and they will want to know why. If configuration allows, trusted users who were formerly allowed to post can be added to the Poster List to work around the new restrictions. It's a good idea to take some proactive measures such as notifying users by posting an message explaining the changes and the reason why the changes are being implemented. You shouldn't expect this to satisfy every list user but it should help reduce the number of support requests.

If you switch to a List Type that doesn't support raw archives, any existing archives (both raw and web archives) will be permanently deleted and cannot be regenerated. If archiving is later enabled, new archives will be generated but they won't include messages posted previous to this point.

As with any form of tightened access, some users who have had access to the archives in the past will find that they no longer have access and will want to know why. If the ability to subscribe has become more restricted, the ability to access archives will probably become more restricted so that list content, whether accessed through the subscription or through the archives, is only available to certain levels of list users.

Ideally, the level of list user given access to archives should be no lower than the level of user able to subscribe in order to maintain an appropriate level of privacy of list content. Access to raw archives is often more tightly controlled than access to web archives, partly because some messages may be deleted from the web archives to remove blatantly inappropriate content.

This is another case where it is wise to notify users before making the change because list users will expect messages sent to the list to appear immediately in the archives and are likely to interpret the delay as something awry in the system, which means they will contact support. Instant archiving requires more system overhead, so this is a good option for low traffic lists.

This change will be relatively transparent to list users, but the increased consumption of system resources is likely to be visible to system administrators, who could be given a "heads up" in advance. This is a good option for large, active lists.

Only public lists should accept public subscription requests via email. If a list that is currently public is set to disallow public subscription requests, some users who are used to subscribing via email will be inconvenienced by being forced to use other channels to subscribe. Some of these users will be members who subscribe under alternate email addresses, which they may no longer be allowed to use. Depending on the list and organization policy, public users may still be allowed to subscribe through web forms or by sending subscription requests to a moderator.

Public lists may allow public users to subscribe via email. This makes it easy for the public to subscribe and for members and higher-level users to subscribe under alternate email addresses. Members often enjoy the convenience of being able to subscribe temporarily under an alternate address while away from their main address, and to add a new subscription by email when they get a new email account. Since this change makes it easier for users to subscribe, the subscription list should grow and the percentage of public users should expand.

Since disallowing attachments limits list messages to plain text format, most lists should allow attachments. Lists used by site administrators who can communicate effectively in plain text might disallow attachments to keep the list footprint small and eliminate the threat of malware being sent to the list.

This will be a welcome change for most lists, as it allows users to include graphics and include non-Roman characters in their communications, but it will increase the amount of system resources consumed by the list. If this change is made on an existing list, the system administrator should be notified so the file size limit for the list can be increased as needed. Virus scanning should also be enabled for lists that allow attachments.