If a Contact has gone through the optin process but still cannot get Matrix emails, the issue may be that they have marked a previous Matrix email as spam, and their mail client is preventing Matrix emails from making it to their Inbox.
If they go into their Spam or Junk Mail folder in their email program and see a Matrix email, they should be able to select the message and mark it as not spam/tell their mail program to make the sender a trusted sender. Once Matrix is added to an allowed list (or marked as a trusted sender) within their email program, their agent should be able to successfully send them emails from Matrix again.
In this scenario, going through the optin process again will not fix the problem, as they never actually opted out of receiving Matrix emails. It has to do with the fact that they physically marked a Matrix email as spam.
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