To check if this is the case, try visiting the archives of the list (assuming that the list has archives). If the list has no archives, you may have to ask another subscriber. (See Section 3.1 for help in finding the list archives.)
Note: Generally, it is considered impolite to send test messages to the entire list. If you feel a need to test that the list is working and for some reason you cannot simply compose a regular message to the list, it is less disruptive to send a help message to the list request address (LISTNAME-request@DOMAIN) to see if that works, or to contact the list administrator (LISTNAME-owner@DOMAIN) to ask if the list is working.
If your mail provider "bounces" too many messages (that is, it tells Mailman that the message could not be delivered) Mailman eventually stops trying to send you mail. This feature allows Mailman to gracefully handle addresses which no longer exist (for example, the subscriber has found a new internet service provider and forgot to unsubscribe the old address), as well as addresses which are temporarily out-of-service (for example, the subscriber has used up all of the allotted space for his or her email account, or the subscriber's mail provider is experiencing difficulties).
Even if you are unaware of any difficulties with your mail provider, it is a good idea to check this. Some popular webmail providers and internet servers are not as reliable as one might assume, nor is the internet as a whole. You may want to also send yourself a test message from another account or ask a friend to send you a test message to make sure your subscribed address is working.
To check if this may be the reason you are not receiving messages, log in to the your options page (See Section 3.1 for more details on how to do this) and look at your options. There should be one marked "Mail Delivery" - if it is set to "Disabled," set it to "Enabled" to start receiving mail again. (For more instructions on disabling or enabling mail delivery, see Section 7.1.)
Note: Even if you have not been disabled at the time you check, you could be bouncing messages and not have reached the threshold for your subscription to be disabled. You may need to check again.
No matter what many of us would like, the internet is not 100% reliable, nor is it always fast. Sometimes, messages simply take a long time to get to you. Try to be patient, especially if the server is far (in terms of networks, not geography, although often one implies the other) from your internet service provider.
To check if this might be causing your problem, you can try pinging the list server or tracing the route between you and it. (Instructions on how to do this varies from platform to platform, so you may want to use a search engine to find those appropriate for you.)
To test if this is a case, try visiting the list's web interface and try sending a message to LISTNAME-request@DOMAIN with the command "help" (without the quotes) in the Subject:. If neither of these works after a reasonable length of time, this may be the problem. You may wish to contact either the list or site administrator(s).