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If someone reports that they sent an email to you, but you didn't receive it, please get them to forward their email to an alternative address that you can access, then include the headers (or all of the email) in your support ticket.
More than 80% of "email not received" support tickets are later identified as user error at the sender end, which results in the client that created the support ticket being charged for unnecessary support.
If we can see the "sent" email header, we can verify the destination address is correct and also see email details (e.g. sender address and time) that will allow us to search the email server logs. Without this information, it is difficult or even impossible to identify the cause or eliminate potential causes.