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Any emails redirected or forwarded via an OWA rule will count as sent email for the purpose of the rate limit. For example, someone forwards to a gmail account using email rules, if they RECIEVE over 1000 messages they will hit the limit and they will stop receiving email. If they are forwarding to 2 other email accounts, they will his the limit after 500 messages, and so forth.
To avoid this issue with the rate limit, forwarding should be set up at the mailbox level via Tufts Tools.