Allow headers of emails to be manipulated more easily? (changed, not duplicated)

rubyonrails-talk
1

e.g.

if I do:

headers["List-Unsubscribe"] = "<mailto:contact@example.com?subject=unsubscribe>"
headers["List-Unsubscribe"] += ", <#{unsubscribe_url}>" if unsubscribe_url

I get an error.

And if I do (simplified example):

headers["List-Unsubscribe"] = "<mailto:contact@example.com?subject=unsubscribe>"
headers["List-Unsubscribe"] = "<#{unsubscribe_url}>" if unsubscribe_url

I get two headers instead of one

wouldn’t it make sense to be able to edit headers? and to not have duplicates (breaking change I guess)?