The size of the message you are trying to send exceeds a temporary size limit of the server. The message was not sent; try to reduce the message size or wait some time and try again. The server responded: 4.5.3 Error: too many recipients.
We set this in main.cf:
We didn't specify it before and the default is said to be 0/unlimited and it still didn't change anything.
The real solution is actually in the smtpd_recipient_limit (set it to however many people you were e-mailing at once, this could be important for large organizations or companies as some still do BCC thousands of people even though mailing lists/aliases/groups are preferable):
Just reload postfix to make it take effect (service postfix reload) you don't need to restart the entire server.
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