To my knowledge you can only select multiple contacts to send a Sales Insight email via Views (200 selectable at a time) and search results (25 selectable at a time). Also, according to the Sending a Marketo Email with Sales Insight help article, the maximum limit for the number of Sales Insight emails sent from Salesforce at one time is 200.
Can you expand on how you added a "mass email button" on your Campaigns that is tied to the Marketo Sales Insight function?
Thanks for the response, i'll give you a little back ground info first so you understand how I ended up in the campaign area.
When we installed Sales Insight one of our key things with the Standard Mass Email functionality was that it did not meet our business requirements for Mass Email. As a global org we have SLA's in place with other countries to restrict certain users/countries/profiles from the ability to send Mass Email, but as we know as soon as you put that on the List View layouts it's open to anybody. (restricting the ability for our users to create list views was not really an option).
So I have a skilled developer in my team who cloned the button and gave it a tweak so only certain profiles can use Mass Email and it is strictly based on ownership as welll. We use a Controller to manage who can use the functionality and it works well and is very easy to maintain.
So my developer pretty much followed the same principal, created a new list button on campaigns using execute java script behaviour and just pointed it to get record id's from the Campaign object.
Testing so far has resulted in successful sends, I just need to get it to send to more than 200 otherwise it's pointless going down this track.
I'll keep testing some more and see if I can send to 201 contacts, if that works then I know there is not a limit.
If your custom button is ultimately hooking into Marketo's standard Send Marketo Email function, it's going to be subject to the 200 email limit. There may be an API call you can use to avoid this or a way to modify the limit. You should open a case with Marketo tech support.
It's fine if we haeve to use some crazy workaround. I just posted a discussion about this here, if you have an answer...
One rule, though: There is one rule: you're not allowed to select them all from a report. This is because giving the sales reps the ability to do that also opens up a wide range of other permissions that they should not have.