"Would the fact that commercial customer provided the financial institution with their email be enough for implicit consent?"
That doesn't sound like it completes an agreement, a meeting with both parties consent, unless you state - by providing your email you agree to... but that could be riddled with issues as you need to know who, what, where and when that this person is able to contract, as an example. Just the way the question was posed it gives the impression that you want to force the person into the agreement, in potentially a deceptive manner. You don't want that - you want a clean agreement with an understanding of terms by all parties.
My opinions are not necessarily my employers.
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell