Mimecast Signature - MCSpamSignature.sa.s.39.5 - Explanation

firefoxchris used Ask the Experts™
Hi All,

I client recently had one of our emails rejected (html email with invoice pdf attached), all clean.

I asked them to look into it and they found it in their external Minecast spam trap. The rejection information supplied is..

Rejection Type: 14080
Rejection Description: Spam Signature Description
Rejection Information: MCSpamSignature.sa.s.39.5

We don't have any more information than that. I've done some Googling around but cant find any details of what MCSpamSignature.sa.s.39.5 relates to and as we don't have Mimecast I cant investigate on our own systems.

Does anyone know what this relates to?

Many thanks in advance!
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We use MC, but I don't know that we even have access to what each specific rule is. My best suggestion is for the client to contact MC and have them figure out why it thinks your email is spam and then you would know what to do to fix it.  Another option would be for them to whitelist all emails coming from you, which is pretty easy to do.  They may not what to, depending on their specific policies, but we've done it here for some companies that we highly trust and that usually solves any similar issues.


Thanks jhyiesla - My client is an employee of a larger organisation that wont' have access to contact Mimecast unfortunatly. He has whitelisted us but im more worried about other organisations that are clients of ours that may have the same issue.

No one wants invoices going missing :)
That's always possible... however, I would guess that if he has the ability to get into the MC portal to whitelist your company, he would also have the ability to open a support ticket with them. Minimally, I'd think he'd have the ability to contact his IT department who would then be able to contact MC. This is a legitimate problem and asking these kinds of questions should be possible... but of course I'm not them. Having said that, I'm not sure that MC would even give away that info as it may make it possible for a spammer to take advantage of that knowledge.
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I imagine this will need to go up his management chain to be authorised to send a Mimecast support ticket. As they're a client they dont really have a vested interest which is why I was looking for a technical explanation or someone who had experienced a similar issue.
Understand...whitelist, which has already been done, is probably the best solution. Again, not sure how much info MC would give on a specific signature as that potentially limits its effectiveness. Sorry, I can't add any thing else to the conversation.


I'd mainly like to know if it is an email Content problem, or aother technical issue like SPF, DKIM etc - all looks ok our end.
From working with the MC system for about 4 years, I say there's a high probability that the issue is NOT at your end from an infrastructure standpoint. I'm betting that if you just sent your contact a regular "Hi how are you" email it would get through just fine.  Then I'd send him one with the formatting that you used in the one that gets blocked, but again, without the attachment. If that one fails to get through, then the rule is classifying the email as spam and it's just the MC rule interpreting your formatting. and whitelisting is problaby the best way to solve it.

If that one does get through and then you send one with the attachment and if it fails, then there's either something about the attachment that MC doesn't like or they have blocked PDF files into their system - which is odd, but not unheard of.

If the PDF file fails, try sending some generic document as a PDF.  If that also fails, but everything without a PDF has succeeded, then most likely they're just blocking PDF files.  If your regular PDF file fails and if a generic one fails, you might want to try zipping the PDF file or even just changing the extender on the PDF file to PDx and then try sending it and he can rename it or unzip it when he gets it.

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