If you are using the native integration, it doesn't really work like that (at least from past experience). If you want to only sync a selective set of contacts you would likely have better luck using a 3rd party integration or even the Zapier connection. In that scenario, you may not even require the use of a workflow.
Josh
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Josh Curcio HubSpot support and inbound marketing for OEMs, contract manufacturers, and industrial suppliers. HubSpot Diamond Partner & HubSpot Certified Trainer
It looks like the Mailchimp-HubSpot integration is pretty limited in terms of contact syncing. Looking at this integration guide from HubSpot, you can have contact automatically added to lists in Mailchimp when they fill out pop-up forms. Beyond that, it doesn't look like there's native integration functionality to sync HubSpot contacts to Mailchimp.
You may have more luck with Zapier (it looks like you can add a tag and such in Mailchimp based on actions in HubSpot), so I would explore that opportunity to see if it'll better fit your use case.
What @Josh and @jolle said. And if you're still looking for a 3rd party integration then I'd like to plug Outfunnel's (where I work) HubSpot - Mailchimp integration because it does exactly what you're looking for. Namely - it syncs contacts from a HubSpot List (or several Lists) to a Mailchimp Audience (or multiple Audiences). It supports mapping almost all types of custom fields and it even syncs email engagement back to HubSpot. If this sounds interesting you can learn more here.
What @Josh and @jolle said. And if you're still looking for a 3rd party integration then I'd like to plug Outfunnel's (where I work) HubSpot - Mailchimp integration because it does exactly what you're looking for. Namely - it syncs contacts from a HubSpot List (or several Lists) to a Mailchimp Audience (or multiple Audiences). It supports mapping almost all types of custom fields and it even syncs email engagement back to HubSpot. If this sounds interesting you can learn more here.
It looks like the Mailchimp-HubSpot integration is pretty limited in terms of contact syncing. Looking at this integration guide from HubSpot, you can have contact automatically added to lists in Mailchimp when they fill out pop-up forms. Beyond that, it doesn't look like there's native integration functionality to sync HubSpot contacts to Mailchimp.
You may have more luck with Zapier (it looks like you can add a tag and such in Mailchimp based on actions in HubSpot), so I would explore that opportunity to see if it'll better fit your use case.
If you are using the native integration, it doesn't really work like that (at least from past experience). If you want to only sync a selective set of contacts you would likely have better luck using a 3rd party integration or even the Zapier connection. In that scenario, you may not even require the use of a workflow.
Josh
Did this post help solve your problem? If so, please mark it as a solution.
Josh Curcio HubSpot support and inbound marketing for OEMs, contract manufacturers, and industrial suppliers. HubSpot Diamond Partner & HubSpot Certified Trainer