You can use CrowdMail Email List Forms to directly subscriber or unsubscribe your mail subscription from website, for your end customers.
For this feature to work, Email List Forms code can be found under each email list. You need to go to particular email list from all email list dashboard and then, from email list dashboard click on “Forms Tools”.
There you can find embed and iframe codes for subscribe and unsubscribe forms of particular email list.
You can use this email list form inside website form building tools, email capture plugins, addons or directly on website to receive the email subscriptions inside the particular email list seamlessly.
You will need to add custom css styles to make this form look goon according to the color scheme of your website.