Error writing message: File too large

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These are primarily notes This is probably not going to be complete in any real sense, and exists to contain bits of useful information.

A postfix error that occurs when a user's mailbox is full.

Regularly caused by cronjob output, particularly when there are systematic errors in the cron job that lead to long and frequent email reports.

mailbox_size_limit and virtual_mailbox_limit may be relevant.

You can use

postconf | egrep '(mailbox_size_limit|virtual_mailbox_limit)'

...to see what size they are currently set at, which is probably 50MB.

Set this to a higher limit (in your .cf files), or even to 0 to remove limits.