...
Email accounts that send email to more than 1000 people within a 24 hour period will be blocked from sending email. Some emails existing email addresses have been whitelisted (for example announcement elists).
If a user needs to temporarily send an email to more than 1000 people in 24 hours, they should contact IT@tufts.edu in order to request a 24 hour allowance. If someone will need to sent large amounts of email regularly, another account should be set up for that purpose and the user's IT department should email IT@tufts.edu in order to whitelist that account.If you believe someone's issue with sending email is related to the rate limit, please include the full headers when submitting the ticket to IT@tufts.edu so that the issue can be resolved more quickly.
...
To avoid this issue with the rate limit, forwarding should be set up at the mailbox level via Tufts Tools. Users can change their forwarding settings at https://tuftstools.tufts.edu/cgi-bin/forward
Removing Rate Limit (Exchange On Prem Only)
To remove the limit, you have to remove the max recipient limit from Exchange Management Console, and then run a command in the shell to put the mailbox in a different policy. This can be done in any order.
Exchange Management Console:
Open up Mailbox Properties in Exchange.
Select Mail Flow Settings tab.
Delivery Options → Properties
Remove check for Maximum Recipients.
Exchange Shell:
Set-Mailbox -Identity UTLN -ThrottlingPolicy HighVolumePolicy