I suspect its a problem with the email server getting blacklisted for spam from time to time. We're on shared hosting with some unknown number of other people. If one of those accounts gets used to send out spam, everyone on the server becomes unable to send email and we won't necessarily know anything has gone wrong unless someone tells us they didn't get the email. The Happy Birthday emails come from the same account as the registration stuff so I guess its working at the moment at least.
Manually setting people to the registered users group is the usual fix if the email won't go.
Manually setting people to the registered users group is the usual fix if the email won't go.
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