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It is probable that your 'error' on scan-to-email operations involving over 12 pages at once, is related to the maximum size your email account can send... or perhaps, on the Scan To Memory setting value on our K-M BizHub printer's own settings.
If the first is the problem, I would advise you to scan at a lower dpi setting, or lower resolution. Go into your K-M BizHub printer's settings or options.
Then look for a setting on Resolution (of Scanning or of Scans), or a setting for D.P.I. (dots per inch) or similar. Set it to a lower value.
This will make the resultant file somewhat smaller, and perhaps within the limits (on size of attached file) set by your email account.
If the second is the problem, go into your printer's Options or Settings.
Look for a Scan To Memory setting. Disable it. Try the scan-to-email operation again.