Import contact to Mailhimp after Contact Form 7 send
Problem: We use Contact Form 7 and if user checked special checkbox, data from form pass to Mailchimp.
Solution: We can use one of plugins:
Contact Form 7 MailChimp Extension - all good, but it has limited quantity fields, that we can pass to Mailchimp: 10 custom fields + 2 fields (email and first/last name). You can indicate fields arbitrarily in CF7, and on options page tell how field from CF7 fit MC. Checkbox for subscribe [opt-in]. If you have simple form that this plugin it's best bet.
MailChimp for WordPress - doesn't has fields limit. In CF7 should use specifical names like mc4wp-[field-name-in-mailchimp-list] e.g., mc4wp-FNAME. If you have few contact forms and Mailchimp lists, you should in each contact form use hiden field like
<input name="_mc4wp_lists" type="hidden" value="123abc456def" />
, where 123abc456def - Mailchimp list ID (More info). You can try this:
[hidden _mc4wp_lists "123abc456def"]