We're currently implementing Marketo at my current company and our IT does not want to whitelist the shared IP addresses, as it masks other issues. However, we also use mimecast, so most of our test and actual email sends to ourselves internally are bouncing due to spamcop blacklists.
Are there any other options to resolve this issue besides a dedicated IP?
The most accurate way to whitelist is based on DKIM signature: it can't be forged by outsiders, nor shared by other tenants on your shared Marketo instance.
However, aside from the technical difficulty (IT may not have a way of treating signed mail from certain domains differently) it's still the case that you're skipping spam checks that would otherwise help you diagnose deliverability probs (if it uses the same signing From: domain and thus same DKIM private key).
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