What do you include on your contact sign-up?

Hi everyone,

Just looking to get an idea of what mandatory and optional fields most people have on their contact sign-up on their websites (eg. for newsletter, campaigns etc.). 

We've currently got first name, last name, email address and postcode as mandatory, and telephone as optional. 

I've been asked to add 1st line of address as another optional field, but I'm concerned this will put people off from signing up as the form is becoming quite long and I don't want potential subscribers to be overwhelmed by the number of fields, even though this would be an optional field. 

What are your opinions on what's the right amount of information to ask for at point of subscription? And do you have any suggestions on how else we could go about gathering data if this isn't the best way?