Users can subscribe via link http://visitor.constantcontact.com/email.jsp?m=110****** from my site.
But how can I open the subscription form with contained email input?
I try to add parameter in URL like &emailAddrfirstname.lastname@example.org but it doesn't work.
We do not allow that form to be pre-populated. I will send this feedback to the Contact Management development team. If you are looking to have a more customized or perscriptive flow for signing up, the only way currently is to develop a custom signup form using our API. This does require web development skills.
Thanks for the additional feedback. Have forwarded this along to our Contact Management team. They will as always evaluate future feature development based on our user feedback. While we have definitely gotten requests for this over the years, it has been fairly sporadic and hasn't climbed up high on the priority list based on the volume of feedback.