Adds the settings:
raw_email_max_length, raw_rejected_email_max_length, delete_rejected_email_after_days.
These settings control retention of the "raw" emails logs.
raw_email_max_length ensures that if we get incoming email that is huge we will truncate it removing uploads from the raw log.
raw_rejected_email_max_length introduces an even more aggressive truncation for rejected incoming mail.
delete_rejected_email_after_days controls how many days we will keep rejected emails for (default 90)
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