That setting won't stop much spam anyway so no need to have it enabled. Alternatively you could add the sender address to the exception list to exclude it from compliance checks.

I have an office phone system on which monitoring was enabled yesterday which routinely sends a status report to the support company via SMTP.  The MercuryS log shows them being rejected per the following entry:

555 Message rejected: site policy requires all mail to be in valid MIME format.

Would disabling the "Refuse non-MIME messages" setting remedy that and, if so, are there any issues to consider before doing so?